bp2build support for stem

By default, the artifacts generated by cc_binary and cc_library in Soong
track the module name. But Soong supports overidding this using the stem
property. e.g.
```
cc_library {
  name: "foo.1.2",
  stem: "foo",
}
```
will generate foo.so

This CL adds this property to bp2build

Test: bp2build unit tests
Bug: 240563612
Change-Id: I1dfed870d5bad450511b72c397d2355c01fa3b60

cc/library.go

@@ -408,6 +408,7 @@ func libraryBp2Build(ctx android.TopDownMutatorContext, m *Module) {
 		sharedTargetAttrs.Stubs_symbol_file = compilerAttrs.stubsSymbolFile
 	}
 
+	sharedTargetAttrs.Stem = compilerAttrs.stem
 	sharedTargetAttrs.Suffix = compilerAttrs.suffix
 
 	for axis, configToProps := range m.GetArchVariantProperties(ctx, &LibraryProperties{}) {
@@ -2987,6 +2988,7 @@ func sharedOrStaticLibraryBp2Build(ctx android.TopDownMutatorContext, module *Mo
 
 			Features: *features,
 
+			Stem:   compilerAttrs.stem,
 			Suffix: compilerAttrs.suffix,
 
 			bazelCcHeaderAbiCheckerAttributes: bp2buildParseAbiCheckerProps(ctx, module),
@@ -3072,6 +3074,7 @@ type bazelCcLibrarySharedAttributes struct {
 
 	Inject_bssl_hash bazel.BoolAttribute
 
+	Stem   bazel.StringAttribute
 	Suffix bazel.StringAttribute
 
 	bazelCcHeaderAbiCheckerAttributes