runtime(vim): Cleanup syntax tests

Improve formatting and naming consistency of the syntax tests.

closes: #17850

Signed-off-by: Doug Kearns <dougkearns@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/syntax/testdir/input/vim_new.vim

@@ -1,13 +1,16 @@
 vim9script
+# Vim :new command and class constructors
+# TODO: move to vim9_constructor and create new vim_ex_new and vim9_ex_new
+#       tests
+
 
-# Vim :new command and class constructors.
 class Test
-	def new()
-	enddef
-	def newOther()
-	enddef
-	def newyetanother()
-	enddef
+  def new()
+  enddef
+  def newOther()
+  enddef
+  def newyetanother()
+  enddef
 endclass
 
 Test.new()
@@ -15,3 +18,4 @@ Test.newOther()
 Test.newyetanother()
 new
 quit
+