Add RuleBuilder helper functions for built and prebuilt tools

Replace the common pattern of:
cmd.Tool(ctx.Config().HostToolPath(ctx, "tool"))
with:
cmd.BuiltTool("tool")

And similarly for PrebuiltBuildTool.

Test: m checkbuild
Change-Id: I7d63188505362c7df6a3b3e7330b4a2cca5a2409
diff --git a/java/java.go b/java/java.go
index 7c84e76..476aedc 100644
--- a/java/java.go
+++ b/java/java.go
@@ -2094,14 +2094,14 @@
 
 		// use zip2zip to uncompress classes*.dex files
 		rule.Command().
-			Tool(ctx.Config().HostToolPath(ctx, "zip2zip")).
+			BuiltTool(ctx, "zip2zip").
 			FlagWithInput("-i ", inputJar).
 			FlagWithOutput("-o ", temporary).
 			FlagWithArg("-0 ", "'classes*.dex'")
 
 		// use zipalign to align uncompressed classes*.dex files
 		rule.Command().
-			Tool(ctx.Config().HostToolPath(ctx, "zipalign")).
+			BuiltTool(ctx, "zipalign").
 			Flag("-f").
 			Text("4").
 			Input(temporary).