sanitizer_common: introduce kInvalidTid/kMainTid

Currently we have a bit of a mess related to tids:
 - sanitizers re-declare kInvalidTid multiple times
 - some call it kUnknownTid
 - implicit assumptions that main tid is 0
 - asan/memprof claim their tids need to fit into 24 bits,
   but this does not seem to be true anymore
 - inconsistent use of u32/int to store tids

Introduce kInvalidTid/kMainTid in sanitizer_common
and use them consistently.

Reviewed By: vitalybuka

Differential Revision: https://reviews.llvm.org/D101428