Add ability to automatically chaining the bridging headers discovered from all
dependencies module when doing swift caching build. This will eliminate all
implicit bridging header imports from the build and make the bridging header
importing behavior much more reliable, while keep the compatibility at maximum.
For example, if the current module A depends on module B and C, and both B and
C are binary modules that uses bridging header, when building module A,
dependency scanner will construct a new header that chains three bridging
headers together with the option to build a PCH from it. This will make all
importing errors more obvious while improving the performance.
Improve caching related tests to make them faster and test the situation
closer to what actually happens during explicit module build. Most
noticable changes are:
* Avoid swift stdlib dependency during the tests to save time
* Use dependency scanner output to construct test cases
* Update old test cases that try to simulate caching from file system
inputs to using only CAS inputs.
Change how cached diagnostics are stored inside the CAS. It used to be
stored as a standalone entry for a frontend invocation in the cache and
now it is switched to be associated with input files, stored together
with other outputs like object files, etc.
This enables cleaner Cache Replay APIs and future cached diagnostics
that can be splitted up by file contribution.
Allow `-typecheck-module-from-interface` using explicit module instead
of building implicit module.
This setups swift-frontend to accept explicit module build arguments and
loading explicit module during verifying. SwiftDriver needs to setup
correct arguments including the output path for swift module to fully
enable explicit module interface check.
