Soong: support Errorprone javacflags

Add support for an errorprone block in Java modules that accepts
additional javacflags for the errorprone build.

Sample:

    errorprone: {
        javacflags: ["-Xep:EqualsNaN:WARN"],
    },

Bug: 72004718
Test: m RUN_ERROR_PRONE=true
Test: manual - add block with ERROR to a project
Test: androidmk_test
Change-Id: I502248fe76c26aa19102f413af72a7324c35b7f4

java/builder.go

@@ -155,6 +155,8 @@ type javaBuilderFlags struct {
 	aidlFlags     string
 	javaVersion   string
 
+	errorProneExtraJavacFlags string
+
 	kotlincFlags     string
 	kotlincClasspath classpath
 
@@ -210,6 +212,14 @@ func RunErrorProne(ctx android.ModuleContext, outputFile android.WritablePath,
 		ctx.ModuleErrorf("cannot build with Error Prone, missing external/error_prone?")
 	}
 
+	if len(flags.errorProneExtraJavacFlags) > 0 {
+		if len(flags.javacFlags) > 0 {
+			flags.javacFlags = flags.errorProneExtraJavacFlags + " " + flags.javacFlags
+		} else {
+			flags.javacFlags = flags.errorProneExtraJavacFlags
+		}
+	}
+
 	transformJavaToClasses(ctx, outputFile, -1, srcFiles, srcJars, flags, nil,
 		"errorprone", "errorprone", errorprone)
 }