Fix c-ts-mode indentation for statement after preproc (bug#61893)

Fix c-ts-mode indentation for statement after preproc (bug#61893)

Originally our c-ts-mode--anchor-prev-sibling only specially handled
labeled_statements, now we add special case for preproc in the similar
fasion: instead of using the preproc directive as anchor, use the last
statement in that preproc as the anchor. Thus effectively ignore the
preproc.

There should be an accompanying test, but there are some problem in
the elif preproc directive indent so it would pass, we'll add the test
when that is fixed.

* lisp/progmodes/c-ts-mode.el:
(c-ts-mode--anchor-prev-sibling): Add special case for preproc
directives.