runtime(syntax-tests): Break up non-ASCII over-75-byte-long lines

And anticipate occasional multibyte line wrapping owing to:
> A poorly rendered line may otherwise become wrapped when enough of
> spurious U+FFFD (0xEF 0xBF 0xBD) characters claim more columns than
> are available (75) and then invalidate line correspondence under test.

Observe that for "vim_ex_command.vim" another workaround is
chosen: the long line containing an only multibyte character
near its EOL is conversely made longer by padding and moving
the character to a separate _tail_ part of the wrapped line.
That is, the _head_ part of the line is all ASCII characters
and the wrapped _tail_ part is a mix of various characters
whose total byte count is within bounds.

Other unmodified tracked files of interest:
  java_lambda_expressions.java,
  java_lambda_expressions_signature.java,
  java_numbers.java,
  markdown_conceal.markdown,
  vim9_generic_function_example_set.vim

Also, remove stray U+FFFC (0xEF 0xBF 0xBC) characters.

Related to #16559 and #17704.

Reference:
https://github.com/vim/vim/blob/0fde6aebddef5cb0428e85040994ba45e55cba99/runtime/syntax/testdir/README.txt#L120-L123

closes: #17868

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

runtime/syntax/testdir/input/vim_ex_function.vim

@@ -259,7 +259,7 @@ endfunction
 
 " Issue https://github.com/vim/vim/pull/17420#issuecomment-2927798687
 " (function named /s:fu%\[nction]/)
-
+
 func! s:func(_, func)
     return a:func
 endfunc