Cleans up build scripts (#5097)

* Cleans up build scripts

* Adds back removeDir

build/shared.mjs

@@ -0,0 +1,90 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+// @ts-check
+
+import { dirname, join } from 'path';
+import { fileURLToPath } from 'url';
+import { readdirSync } from 'fs';
+
+/**
+ * @param {string} filePath
+ * @param {string} newExt
+ */
+export function changeExt(filePath, newExt) {
+	const idx = filePath.lastIndexOf('.');
+	if (idx === -1) {
+		return filePath + newExt;
+	} else {
+		return filePath.substring(0, idx) + newExt;
+	}
+}
+
+export function getNlsEntryPoints() {
+	const nlsDir = dirname(fileURLToPath(import.meta.resolve('monaco-editor-core/esm/nls.messages.en.js')));
+	const nlsFiles = readdirSync(nlsDir)
+		.filter(file => file.startsWith('nls.messages.') && file.endsWith('.js'))
+		.reduce((acc, file) => {
+			// @ts-ignore
+			acc[file] = join(nlsDir, file);
+			return acc;
+		}, {});
+	return nlsFiles;
+}
+
+const root = join(import.meta.dirname, '../');
+
+const mappedPaths = {
+	[join(root, 'node_modules/monaco-editor-core/esm/')]: '.',
+	[join(root, 'node_modules/')]: 'external/',
+	[join(root, 'monaco-lsp-client/')]: 'external/monaco-lsp-client/',
+	[join(root, 'src/')]: 'vs/',
+};
+
+/**
+ * @param {string} moduleId
+ * @param {string} newExt (with leading .)
+ * @returns {string | undefined}
+ */
+export function mapModuleId(moduleId, newExt) {
+	for (const [key, val] of Object.entries(mappedPaths)) {
+		if (moduleId.startsWith(key)) {
+			const relativePath = moduleId.substring(key.length);
+			return changeExt(join(val, relativePath), newExt);
+		}
+	}
+	return undefined;
+}
+
+/** @return {import('rollup').Plugin} */
+export function dtsDeprecationWarning() {
+	return {
+		name: 'add-dts-deprecation-warning',
+		generateBundle(options, bundle) {
+			for (const fileName in bundle) {
+				const file = bundle[fileName];
+				if (file.type === 'chunk' && fileName.endsWith('.d.ts')) {
+					let content = file.code.toString();
+					content = content + `
+declare namespace languages {
+	/** @deprecated Use the new top level "css" namespace instead. */
+	export const css: { deprecated: true };
+
+	/** @deprecated Use the new top level "html" namespace instead. */
+	export const html: { deprecated: true };
+
+	/** @deprecated Use the new top level "json" namespace instead. */
+	export const json: { deprecated: true };
+
+	/** @deprecated Use the new top level "typescript" namespace instead. */
+	export const typescript: { deprecated: true };
+}
+`;
+					file.code = content;
+				}
+			}
+		}
+	};
+}