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/dumps/java_methods_indent2_04.dump

@@ -14,7 +14,7 @@
 | +0#00e0e07&@1|p+0#00e0003&|u|b|l|i|c| +0#00e0e07&|S|t|r|i|n|g| |t|o|S|t|r|i|n|g|(|)| +0#0000000&|{+0#00e0e07&| +0#0000000&|r+0#af5f00255&|e|t|u|r|n| +0#0000000&|(|S|t|r|i|n|g|)| |"+0#e000002&|I|n|d|e|n|t|2|M|e|t|h|o|d|s|T|e|s|t|s|"|;+0#0000000&| |}+0#00e0e07&| +0#0000000&@5
 |}+0#00e0e07&| +0#0000000&@73
 @75
-|e+0#00e0003&|n|u|m| +0#0000000&|𝓔| @68
+|e+0#00e0003&|n|u|m| +0#0000000&|E|2| @67
 |{+0#00e0e07&| +0#0000000&@73
-@2|@+0#e000e06&|S|u|p@1|r|e|s@1|W|a|r|n|i|n|g|s|(+0#0000000&|"+0#e000002&|b|e|s|p|o|k|e|"|)+0#0000000&| |A|(|"+0#e000002&|𝗔|"|)+0#0000000&|,| @36
+@2|@+0#e000e06&|S|u|p@1|r|e|s@1|W|a|r|n|i|n|g|s|(+0#0000000&|"+0#e000002&|b|e|s|p|o|k|e|"|)+0#0000000&| |A|(|"+0#e000002&|a|"|)+0#0000000&|,| @36
 @57|7|3|,|3| @9|9|1|%|