Verify that every test file which references a harness file using the
"includes" directive also contains at least one reference to a value
defined in the harness file.
To support this check, extend each harness file with a list of values
which it defines.
typeCoercion.js is included in several tests which are not marked as `features: [BigInt]`.
Since BigInt is new feature, we should not make the above unrelated tests failed due to
lack of BigInt syntax support.
Close#1252.