Implement stubs.symbol_file and stubs.versions for cc_library_shared bp2build.

This CL turns the stubs.symbol_file and stubs.versions properties into
stubs_symbol_file and stubs_version attributes on the cc_shared_library
target. See associated build/bazel change on how these attributes are
used to generate stub libraries.

Bug: 207812332

Test: New tests
Test: CI
Change-Id: Ie23eafb9903a131d92ff4e251215e998cea0a763

bp2build/conversion_test.go

@@ -102,6 +102,14 @@ func TestCreateBazelFiles_Bp2Build_CreatesDefaultFiles(t *testing.T) {
 			dir:      "product_config",
 			basename: "soong_config_variables.bzl",
 		},
+		{
+			dir:      "api_levels",
+			basename: GeneratedBuildFileName,
+		},
+		{
+			dir:      "api_levels",
+			basename: "api_levels.json",
+		},
 	}
 
 	if len(files) != len(expectedFilePaths) {