runtime(java): Improve the recognition of the "style" method declarations

- Request the new regexp engine (v7.3.970) for [:upper:] and
  [:lower:].

- Recognise declarations of in-line annotated methods.

- Recognise declarations of _strictfp_ methods.

- Establish partial order for method modifiers as shown in
  the MethodModifier production; namely, _public_ and
  friends should be written the leftmost, possibly followed
  by _abstract_ or _default_, or possibly followed by other
  modifiers.

- Stop looking for parameterisable primitive types (void<?>,
  int<Object>, etc., are malformed).

- Stop looking for arrays of _void_.

- Acknowledge the prevailing convention for method names to
  begin with a small letter and for class/interface names to
  begin with a capital letter; and, therefore, desist from
  claiming declarations of enum constants and constructors
  with javaFuncDef.
  Rationale:
    + Constructor is distinct from method:
      * its (overloaded) name is not arbitrary;
      * its return type is implicit;
      * its _throws_ clause depends on indirect vagaries of
        instance (variable) initialisers;
      * its invocation makes other constructors of its type
        hierarchy invoked one by one, concluding with the
        primordial constructor;
      * its explicit invocation, via _this_ or _super_, can
        only appear as the first statement in a constructor
        (not anymore, see JEP 447); else, its _super_ call
        cannot appear in constructors of _record_ or _enum_;
        and neither invocation is allowed for the primordial
        constructor;
      * it is not a member of its class, like initialisers,
        and is never inherited;
      * it is never _abstract_ or _native_.
    + Constructor declarations tend to be few in number and
      merit visual recognition from method declarations.
    + Enum constants define a fixed set of type instances
      and more resemble class variable initialisers.

Note that the code duplicated for @javaFuncParams is written
keeping in mind for g:java_highlight_functions a pending 3rd
variant, which would require none of the :syn-cluster added
groups.

closes: #14620

Signed-off-by: Aliaksei Budavei <0x000c70@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/syntax/testdir/input/java_methods_indent.java

@@ -0,0 +1,70 @@
+// VIM_TEST_SETUP let g:java_highlight_functions = 'indent'
+
+
+import java.lang.annotation.Target;
+
+abstract class IndentMethodsTests
+{ // DO NOT retab! THIS FILE; REMEMBER ABOUT testdir/ftplugin.
+  protected IndentMethodsTests() { }
+
+  record Τʬ<α>(α a) { }
+
+  enum 𝓔
+  {
+        A("𝕬"), B("𝕭"), C("𝕮"), D("𝕯"),
+        E("𝕰"), F("𝕱"), G("𝕲"), H("𝕳");
+        final String 𝐬;
+        private 𝓔(String 𝐬) { this.𝐬 = 𝐬; }
+  }
+
+  @Target(java.lang.annotation.ElementType.METHOD)
+  @java.lang.annotation.Repeatable(Tɐggablɘs.class)
+  @interface Tɐggablɘ
+  {
+        String[] value() default "";
+  }
+
+  @Target(java.lang.annotation.ElementType.METHOD)
+  @interface Tɐggablɘs
+  {
+        Tɐggablɘ[] value();
+  }
+
+  interface Stylable<Α>
+  {
+        default void ascii$0_() { }
+        default Α μʭʭ$0_() { return null; }
+  }
+
+  @Tɐggablɘ @Tɐggablɘ
+  abstract void ascii$0_();
+
+  @Tɐggablɘ @Tɐggablɘ
+  abstract <α, β> Τʬ<α> μʭʭ$0_(β 𝛽);
+
+  @Tɐggablɘ
+  private native void ascii$1_();
+
+  @Tɐggablɘ
+  private native <α, β> Τʬ<α>[] μʭʭ$1_(
+                        java.util.function.Function<β, Τʬ<α>[]> ƒ);
+
+  static final native synchronized void ascii$98_();
+  static final native synchronized <α, β> Τʬ<α>[][] μʭʭ$98_(
+                        java.util.function.Function<β, Τʬ<α>[][]> ƒ);
+
+  @SuppressWarnings("strictfp")
+  protected static final synchronized strictfp void ascii$99_()
+  { ascii$98_(); }
+
+  @SuppressWarnings("strictfp")
+  protected static final synchronized strictfp <α, β> Τʬ<α>[] μʭʭ$99_(
+                        java.util.function.Function<β, Τʬ<α>[][]> ƒ)
+  {
+    return
+        IndentMethodsTests.<α, β>μʭʭ$98_(ƒ)[0];
+  }
+
+  @Override @SuppressWarnings("cast")
+  public String toString() { return (String) "IndentMethodsTests"; }
+}

runtime/syntax/testdir/input/java_methods_style.java

@@ -0,0 +1,66 @@
+// VIM_TEST_SETUP let g:java_highlight_functions = 'style'
+
+
+import java.lang.annotation.Target;
+
+abstract class StyleMethodsTests
+{
+	protected StyleMethodsTests() { }
+
+	record Τʬ<α>(α a) { }
+
+	enum 𝓔
+	{
+		A("𝕬"), B("𝕭"), C("𝕮"), D("𝕯"),
+		E("𝕰"), F("𝕱"), G("𝕲"), H("𝕳");
+		final String 𝐬;
+		private 𝓔(String 𝐬) { this.𝐬 = 𝐬; }
+	}
+
+	@Target(java.lang.annotation.ElementType.METHOD)
+	@java.lang.annotation.Repeatable(Tɐggablɘs.class)
+	@interface Tɐggablɘ
+	{
+		String[] value() default "";
+	}
+
+	@Target(java.lang.annotation.ElementType.METHOD)
+	@interface Tɐggablɘs
+	{
+		Tɐggablɘ[] value();
+	}
+
+	interface Stylable<Α>
+	{
+		default void ascii$0_() { }
+		default Α μʭʭ$0_() { return null; }
+	}
+
+	@Tɐggablɘ @Tɐggablɘ abstract void ascii$0_(////////////////
+								);
+	@Tɐggablɘ @Tɐggablɘ abstract <α, β> Τʬ<α> μʭʭ$0_(
+			/* TODO: @SuppressWarnings("bespoke")*/ β 𝛽);
+
+	@Tɐggablɘ private native void ascii$1_(/*////////////*/);
+	@Tɐggablɘ private native <α, β> Τʬ<α>[] μʭʭ$1_(
+			java.util.function.Function<β, Τʬ<α>[]> ƒ);
+
+	static final native synchronized void ascii$98_();
+	static final native synchronized <α, β> Τʬ<α>[][] μʭʭ$98_(
+			java.util.function.Function<β, Τʬ<α>[][]> ƒ);
+
+	@SuppressWarnings("strictfp")
+	protected static final synchronized strictfp void ascii$99_()
+	{ ascii$98_(); }
+
+	@SuppressWarnings("strictfp")
+	protected static final synchronized strictfp <α, β> Τʬ<α>[] μʭʭ$99_(
+			java.util.function.Function<β, Τʬ<α>[][]> ƒ)
+	{
+		return
+	StyleMethodsTests.<α, β>μʭʭ$98_(ƒ)[0];
+	}
+
+	@Override @SuppressWarnings("cast")
+	public String toString() { return (String) "StyleMethodsTests"; }
+}