cc: export Stripper struct

The cc stripping logic can be reused for Rust. Export the Stripper
structure for that purpose. Extract the strip-related flags from
builderFlags into StripFlags. Add the method flagsToStripFlags
(similarly to flagsToBuilderFlags).

Add the helper method disableStripping on libraryDecorator.

Test: m
Bug: 153430439
Change-Id: I11aef1abb8d498a4c1672500a7398279edf7f548