[lldb] Extract reproducer providers & co into their own header.

Extract all the provider related logic from Reproducer.h and move it
into its own header ReproducerProvider.h. These classes are seeing most
of the development these days and this reorganization reduces
incremental compilation from ~520 to ~110 files when making changes to
the new header.

GitOrigin-RevId: bb894b97821a1c970ce0c3243aaebbfa94add15c
18 files changed