Mangle exported symbols (#182935)

* Mangle exported functions

For #180461

This prototype tries to mangle exported functions, saving a further 440kb from the bundle size

* Fix missing call

* Also try mangling top level exported consts too

* Fixing errors

* Don't run on build files

* Skip a few more manglings and revert change to namespace

* Skip a few more monaco files

* Also mangle consts that shadow types

This increases savings up to 3325

* Also mangle exported classes

* Skip mangling more localization functions for now

* Opt out pfs

* Update build script

* Run find locations task in parallel

This should speed up compile

* Cleanup before close

* Limit workers to avoid hitting memory limit

* Limit pool size

* Skip one more mangling

* Exclude entrypoints from mangling

* Try to fix web build and clean up code

* Exempt a few more projects

* Exempt another file

* Also exempt html

* Skip mangling ext entrypoints

* Use prefix that can't be confused with rpc calls

* Fix max call stack error

* Switch prefixes

* Don't mangle ambient declarations

* Use correct way of checking modifier flags

* Workaround getCombinedModifierFlags not doing what I'd expect

Maybe needs the checker to be enabled too? Just check parent chain instead for now

* Clean up code and add logic showing how enum mangling could work

* Remove a few more skipMangles

Use entrypoints instead

* Fix entrypoint name

build/lib/mangle/staticLanguageServiceHost.ts

@@ -0,0 +1,62 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import * as ts from 'typescript';
+import * as path from 'path';
+
+export class StaticLanguageServiceHost implements ts.LanguageServiceHost {
+
+	private readonly _cmdLine: ts.ParsedCommandLine;
+	private readonly _scriptSnapshots: Map<string, ts.IScriptSnapshot> = new Map();
+
+	constructor(readonly projectPath: string) {
+		const existingOptions: Partial<ts.CompilerOptions> = {};
+		const parsed = ts.readConfigFile(projectPath, ts.sys.readFile);
+		if (parsed.error) {
+			throw parsed.error;
+		}
+		this._cmdLine = ts.parseJsonConfigFileContent(parsed.config, ts.sys, path.dirname(projectPath), existingOptions);
+		if (this._cmdLine.errors.length > 0) {
+			throw parsed.error;
+		}
+	}
+	getCompilationSettings(): ts.CompilerOptions {
+		return this._cmdLine.options;
+	}
+	getScriptFileNames(): string[] {
+		return this._cmdLine.fileNames;
+	}
+	getScriptVersion(_fileName: string): string {
+		return '1';
+	}
+	getProjectVersion(): string {
+		return '1';
+	}
+	getScriptSnapshot(fileName: string): ts.IScriptSnapshot | undefined {
+		let result: ts.IScriptSnapshot | undefined = this._scriptSnapshots.get(fileName);
+		if (result === undefined) {
+			const content = ts.sys.readFile(fileName);
+			if (content === undefined) {
+				return undefined;
+			}
+			result = ts.ScriptSnapshot.fromString(content);
+			this._scriptSnapshots.set(fileName, result);
+		}
+		return result;
+	}
+	getCurrentDirectory(): string {
+		return path.dirname(this.projectPath);
+	}
+	getDefaultLibFileName(options: ts.CompilerOptions): string {
+		return ts.getDefaultLibFilePath(options);
+	}
+	directoryExists = ts.sys.directoryExists;
+	getDirectories = ts.sys.getDirectories;
+	fileExists = ts.sys.fileExists;
+	readFile = ts.sys.readFile;
+	readDirectory = ts.sys.readDirectory;
+	// this is necessary to make source references work.
+	realpath = ts.sys.realpath;
+}