runtime(java): Stop handpicking syntax groups for @javaTop (#14727)

* runtime(java): Stop handpicking syntax groups for @javaTop

Also:

- Remove the obsolete comment for g:java_allow_cpp_keywords.
- Remove the commented out groups java\%[Debug\]StringError.
- Infer and set the preferred formatting Vim options from
  the modeline.

Since vim-6-0u, non-contained syntax groups can be referred
to by using the "contains=TOP..." argument.

* Set &encoding and &termencoding to "utf-8" for test files

* Limit non-ASCII charset to [§ƒɐɘʬʭΑ-Τα-μ] for test files

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

runtime/syntax/testdir/input/java_methods_style.java

@@ -1,5 +1,5 @@
 // VIM_TEST_SETUP let g:java_highlight_functions = 'style'
-
+// VIM_TEST_SETUP set encoding=utf-8 termencoding=utf-8
 
 import java.lang.annotation.ElementType;
 import java.lang.annotation.Target;
@@ -9,12 +9,12 @@ abstract class StyleMethodsTests
 	// TYPES.
 	record Τʬ<α>(α a) { }
 
-	enum 𝓔
+	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; }
+		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({ElementType.METHOD, ElementType.CONSTRUCTOR})
@@ -50,7 +50,7 @@ abstract class StyleMethodsTests
 	@Tɐggablɘ @Tɐggablɘ abstract void ascii$0_(////////////////
 								);
 	@Tɐggablɘ @Tɐggablɘ abstract <α, β> Τʬ<α> μʭʭ$0_(
-			/* TODO: @SuppressWarnings("bespoke")*/ β 𝛽);
+			/* TODO: @SuppressWarnings("bespoke")*/ β b);
 
 	@Tɐggablɘ private native void ascii$1_(/*////////////*/);
 	@Tɐggablɘ private native <α, β> Τʬ<α>[] μʭʭ$1_(