patch 8.2.0562: Vim9: cannot split an expression into multiple lines

Problem:    Vim9: cannot split an expression into multiple lines.
Solution:   Continue in next line after an operator.

runtime/doc/vim9.txt

@@ -195,6 +195,18 @@ Function call: >
 			arg2
 			)
 
+For binary operators iin expressions not in [], {} or () a line break is
+possible AFTER the operators.  For example: >
+	let text = lead ..
+		   middle ..
+		   end
+	let total = start +
+	            end -
+		    correction
+	let result = positive ?
+			PosFunc(arg) :
+			NegFunc(arg)
+
 Note that "enddef" cannot be used at the start of a continuation line, it ends
 the current function.