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