Replace -bootclasspath and -classpath metalava options with --classpath

Metalava has not differentiated between bootclasspath and classpath for
years so this change replaces the use of the two deprecated single
hyphen options with `--classpath`.

Bug: 295136054
Test: m checkapi
(cherry picked from https://android-review.googlesource.com/q/commit:f8aaaa13f4fb87cc0f7bd5231f2334499d174109)
Merged-In: I3ab20b76a60cab66a27784b7d87a069813d19835
Change-Id: I3ab20b76a60cab66a27784b7d87a069813d19835

java/droidstubs.go

diff --git a/java/droidstubs.go b/java/droidstubs.go
index 1b25883..9379b88 100644
--- a/java/droidstubs.go
+++ b/java/droidstubs.go
@@ -516,12 +516,12 @@
 		FlagWithRspFileInputList("@", android.PathForModuleOut(ctx, "metalava.rsp"), srcs).
 		FlagWithInput("@", srcJarList)
 
-	if len(bootclasspath) > 0 {
-		cmd.FlagWithInputList("-bootclasspath ", bootclasspath.Paths(), ":")
-	}
-
-	if len(classpath) > 0 {
-		cmd.FlagWithInputList("-classpath ", classpath.Paths(), ":")
+	// Metalava does not differentiate between bootclasspath and classpath and has not done so for
+	// years, so it is unlikely to change any time soon.
+	combinedPaths := append(([]android.Path)(nil), bootclasspath.Paths()...)
+	combinedPaths = append(combinedPaths, classpath.Paths()...)
+	if len(combinedPaths) > 0 {
+		cmd.FlagWithInputList("--classpath ", combinedPaths, ":")
 	}
 
 	cmd.Flag("--no-banner").