Add tidy_timeout_srcs property

Similar to `tidy_disabled_srcs`, a `tidy_timeout_srcs` list
can be used to include all source files that took long to compile
with clang-tidy. Files listed in `tidy_timeout_srcs` will not
be compiled by clang-tidy when `TIDY_TIMEOUT` is defined.

Bug: 201099167
Test: TIDY_TIME=90 make droid tidy-soong_subset
Change-Id: Ie0bfda66caae4445d10117ceefa1b5b8c1ecf256