Add support for more operators in check macros

[cschreib]

This PR does the following:

• Add support for using REQUIRE()/CHECK() macros on expressions containing bitwise operators (&, |, ^), and assignments (=, +=, etc.).
• Add missing information to the test events (success/failure/skipped flag and assertion count for test_case_ended, and duration for test_run_ended).
• Enable tests for using small_string and small_vector in constexpr context.
• Some internal refactoring to use clearer names.