rust: strip libraries and binaries

Reuses the cc.Stripper logic. Abstracts Stripper to avoid the spreading
of references to the cc package.

rustc requires unstripped libraries (precisely, with the `.rustc`
section) when building dependent targets. Contrary to cc, the output of
a compiler module will remain unstripped and only an extra build rule
will be added. This rule will be referenced at install time (in
baseCompiler.install or androidmk).

This change drastically reduces the size of the installed libraries:
(unstripped, from out/target/product/crosshatch/system)
$ find . -name \*.dylib.so -print0 | du -c --files0-from=-
149996  total

(stripped, with this change)
$ find . -name \*.dylib.so -print0 | du -c --files0-from=-
42380   total

Bug: 153430439
Test: cd external/rust; mma
Change-Id: I94fd8bbcec97e0610aa325d3db4460be84d01734