[#21853] Adjust Go cross-compile to target entire package (#21854)

This logic was already being applied in the test case but not the general case. Now it is just applied regardless. Instead of targeting a specific main.go file (ex. "foo/main.go") it will now target an entire directory (ex. "foo/.") and get all the other files needed.

sdks/go/pkg/beam/runners/universal/runnerlib/compile.go

@@ -79,10 +79,10 @@ func BuildWorkerBinary(ctx context.Context, filename string) error {
 	log.Infof(ctx, "Cross-compiling %v as %v", program, filename)
 
 	// Cross-compile given go program. Not awesome.
+	program = program[:strings.LastIndex(program, "/")+1]
+	program = program + "."
 	var build []string
 	if isTest {
-		program = program[:strings.LastIndex(program, "/")+1]
-		program = program + "."
 		build = []string{"go", "test", "-c", "-o", filename, program}
 	} else {
 		build = []string{"go", "build", "-o", filename, program}