runtime(java): Recognise text blocks (#14128)

runtime(java): Recognise text blocks (#14128)

Also, accept as valid the space escape sequence `\s`.

Also, consistently use the claimed `javaDebug` prefix for
syntax group definitions kept under `g:java_highlight_debug`.

Since `javaStringError` is commented out for its generality,
let's comment out `javaDebugStringError`, its copy, as well.

References:
https://openjdk.org/jeps/378
https://docs.oracle.com/javase/specs/jls/se17/html/jls-3.html#jls-3.10.7

Closes #10910.

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