Replace android.WriteFile rule with android.WriteFileRule

The android.WriteFile rule takes careful escaping to produce the
right contents.  Wrap it in an android.WriteFileRule that handles
the escaping.

Test: compare all android.WriteFile outputs
Change-Id: If71a5843af47a37ca61714e1a1ebb32d08536c31
diff --git a/java/builder.go b/java/builder.go
index 3043e46..cd35245 100644
--- a/java/builder.go
+++ b/java/builder.go
@@ -572,14 +572,7 @@
 }
 
 func GenerateMainClassManifest(ctx android.ModuleContext, outputFile android.WritablePath, mainClass string) {
-	ctx.Build(pctx, android.BuildParams{
-		Rule:        android.WriteFile,
-		Description: "manifest",
-		Output:      outputFile,
-		Args: map[string]string{
-			"content": "Main-Class: " + mainClass + "\n",
-		},
-	})
+	android.WriteFileRule(ctx, outputFile, "Main-Class: "+mainClass+"\n")
 }
 
 func TransformZipAlign(ctx android.ModuleContext, outputFile android.WritablePath, inputFile android.Path) {