runtime(java): Recognise non-ASCII identifiers (#14543)

runtime(java): Recognise non-ASCII identifiers (#14543)

* runtime(java): Recognise non-ASCII identifiers

Also:

- Remove the already commented out and less general in its
  definition javaFuncDef alternative.

- Stop recognising some bespoke {p,trace} debugging API.

Non-ASCII identifiers have been supported from the outset
of the Java language.

> An _identifier_ is an unlimited-length sequence of _Java
> letters_ and _Java digits_, the first of which must be a
> Java letter.  An identifier cannot have the same spelling
> (Unicode character sequence) as a keyword . . . Boolean
> literal . . . or the null literal . . .
> . . . . . . . .
> Letters and digits may be drawn from the entire Unicode
> character set . . .
> . . . . . . . .
> A Java letter is a character for which the method
> Character.isJavaLetter . . . returns true.  A Java
> letter-or-digit is a character for which the method
> Character.isJavaLetterOrDigit . . . returns true.
> . . . . . . . .
> The Java letters include . . . for historical reasons, the
> ASCII underscore (_) . . . and dollar sign ($) . . .

(Separate syntax tests will be written when particular parts
now touched will have been further improved.)

Reference:
https://javaalmanac.io/jdk/1.0/langspec.pdf [§3.8]

* Take on the maintenance of Java filetype and syntax files

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