runtime(java): Manage byte limits for variable-width lookbehind assertions

runtime(java): Manage byte limits for variable-width lookbehind assertions

Raise the byte limits from 80 to 120 for "javaFuncDef" and
"java*CommentTitle"; and support selecting other arbitrary
values with
------------------------------------------------------------
	let g:java_lookbehind_byte_counts = {
		\ 'javaMarkdownCommentTitle': 240,
	\ }
------------------------------------------------------------

for related groups of syntax definitions, referring to their
names with dictionary keys.

Over-80-Byte-Limit Lookbehind Examples:
https://raw.githubusercontent.com/openjdk/jdk/refs/tags/jdk-24%2B36/src/java.base/share/classes/sun/security/x509/NamedX509Key.java [Lines 43 & 44]
https://raw.githubusercontent.com/openjdk/jdk/refs/tags/jdk-24%2B36/src/jdk.compiler/share/classes/com/sun/tools/javac/util/GraphUtils.java [Line 154]

closes: #17921

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