[lldb] Report clang module build remarks

Update the Clang diagnostic consumer (in ClangModulesDeclVendor) to report
progress on Clang module builds, as both progress events and expression logs.

Module build remarks are enabled by with clang's `-Rmodule-build` flag.

With this change, command line users of lldb will see progress events showing
which modules are being built, and - by how long they stay on screen - how much
time it takes to build them. IDEs that show progress events can show these
updates if desired.

This does not show module-import remarks, although that may be added as a
future change.

Differential Revision: https://reviews.llvm.org/D140056