Tests: Exclude tests based on compilation flags, not API presence

Introduces a new test API, `includesModule`. The method returns whether
a particular module like "ajax" or "deprecated" is included in the current
jQuery build; it handles the slim build as well. The util was created so that
we don't treat presence of particular APIs to decide whether to run a test as
then if we accidentally remove an API, the tests would still not fail.

Fixes gh-5069
Closes gh-5046

build/tasks/build.js

@@ -10,6 +10,7 @@ module.exports = function( grunt ) {
 	const fs = require( "fs" );
 	const path = require( "path" );
 	const rollup = require( "rollup" );
+	const slimBuildFlags = require( "./lib/slim-build-flags" );
 	const rollupFileOverrides = require( "./lib/rollup-plugin-file-overrides" );
 	const Insight = require( "insight" );
 	const pkg = require( "../../package.json" );
@@ -60,7 +61,6 @@ module.exports = function( grunt ) {
 		const done = this.async();
 
 		try {
-			const slimFlags = [ "-ajax", "-callbacks", "-deferred", "-effects", "-queue" ];
 			const flags = this.flags;
 			const optIn = flags[ "*" ];
 			let name = grunt.option( "filename" );
@@ -79,7 +79,7 @@ module.exports = function( grunt ) {
 
 			if ( flags.slim ) {
 				delete flags.slim;
-				for ( const flag of slimFlags ) {
+				for ( const flag of slimBuildFlags ) {
 					flags[ flag ] = true;
 				}
 			}

build/tasks/lib/slim-build-flags.js

@@ -0,0 +1,10 @@
+"use strict";
+
+// NOTE: keep it in sync with test/data/testinit.js
+module.exports = [
+	"-ajax",
+	"-callbacks",
+	"-deferred",
+	"-effects",
+	"-queue"
+];