Add support for Rust C libraries.

Adds the ability for rust modules to be compiled as C libraries, and
allows cc modules to depend on these rust-generated modules. This also
means that soong-rust should not have any dependencies on soong-cc aside
from what's required for testing.

There's a couple small fixes included as well:

 - A bug in libNameFromFilePath that caused issues when library's had
 "lib" in their name.
 - VariantName is removed from rust library MutatedProperties since this
 was unused.

Bug: 140726209
Test: Soong tests pass.
Test: Example cc_binary can include a rust shared library as a dep.
Test: m crosvm.experimental
Change-Id: Ia7deed1345d2423001089014cc65ce7934123da4
diff --git a/rust/config/toolchain.go b/rust/config/toolchain.go
index 328bca3..616d88b 100644
--- a/rust/config/toolchain.go
+++ b/rust/config/toolchain.go
@@ -95,7 +95,7 @@
 	return ".rlib"
 }
 func (toolchainBase) DylibSuffix() string {
-	return ".so"
+	return ".dylib.so"
 }
 
 func (toolchainBase) ProcMacroSuffix() string {