Enable completion of indented hash directives

[Martin521]

The compiler allows preceding whitespace for all hash directives.
FSAC, however, auto-completes hash directives only at the beginning of a line.
This PR enables completion also for indented hash directives.

[baronfel]

Thanks @Martin521! This seems reasonable. I do wonder how much value we get out of this special case instead of just going through the 'normal' "check the parse tree for completion context" stuff we do for all other completions though. That's not a comment on your fix - more the overall reasoning behind why we ever did this split.

[Martin521]

I guess the reason is that the conditional compilation directives (#if/#else/#endif) (and soon probably also #nowarn/#warnon) are not in the parse tree.
(Completion of these short directives has limited value, but since I was looking for places that need to be changed for #warnon, I ended up doing this.)