[dev][Legacy][JS] Split Legacy mode JavaScript into new ResourceLoader module

The collapsible sidebar adds a new JavaScript dependency and behavior to
Latest mode only. There are a number of ways of to make the deviation
but we think now is the time to start splitting by module.

This patch adds a new ResourceLoader module, skins.vector.legacy.js, and
moves the existing JavaScript into it. The old module, skins.vector.js,
has been given a currently matching index.js entry point that references
the collapsible tabs' files by reaching across directories. It's not
quite ideal as usually ResourceLoader modules and directory structures
strive for 1:1 correspondence but this patch makes the bold assertions
that it's better than a file copy, better than a new
"skins.vector.common.js" ResourceLoader module, more compatible than a
symlink, and the existing jQuery tabs implementation will eventually be
replaced in Latest mode.

A "Legacy" module was added instead of a "Latest" with the assumption
that active development should generally be considered "latest" and
Legacy an intentional distinction.

Bug: T246419
Change-Id: I9980403f1ee5897c27ac0331f0b51a5bcbdff778

includes/SkinVector.php

@@ -84,7 +84,7 @@ class SkinVector extends SkinTemplate {
 		$module = $this->isLegacy()
 			? 'skins.vector.styles.legacy' : 'skins.vector.styles';
 		$modules['styles']['skin'][] = $module;
-		$modules['core'][] = 'skins.vector.js';
+		$modules['core'][] = $this->isLegacy() ? 'skins.vector.legacy.js' : 'skins.vector.js';
 
 		return $modules;
 	}

resources/skins.vector.js/index.js

@@ -1,6 +1,6 @@
 var
-	collapsibleTabs = require( './collapsibleTabs.js' ),
-	vector = require( './vector.js' );
+	collapsibleTabs = require( '../skins.vector.legacy.js/collapsibleTabs.js' ),
+	vector = require( '../skins.vector.legacy.js/vector.js' );
 
 function main() {
 	collapsibleTabs.init();

resources/skins.vector.legacy.js/index.js

@@ -0,0 +1,10 @@
+var
+	collapsibleTabs = require( './collapsibleTabs.js' ),
+	vector = require( './vector.js' );
+
+function main() {
+	collapsibleTabs.init();
+	$( vector.init );
+}
+
+main();

skin.json

@@ -67,8 +67,18 @@
 		"skins.vector.js": {
 			"packageFiles": [
 				"resources/skins.vector.js/index.js",
-				"resources/skins.vector.js/collapsibleTabs.js",
-				"resources/skins.vector.js/vector.js"
+				"resources/skins.vector.legacy.js/collapsibleTabs.js",
+				"resources/skins.vector.legacy.js/vector.js"
+			],
+			"dependencies": [
+				"mediawiki.util"
+			]
+		},
+		"skins.vector.legacy.js": {
+			"packageFiles": [
+				"resources/skins.vector.legacy.js/index.js",
+				"resources/skins.vector.legacy.js/collapsibleTabs.js",
+				"resources/skins.vector.legacy.js/vector.js"
 			],
 			"dependencies": [
 				"mediawiki.util"