Use src/ imports in addons; bundle test output via esbuild

Addons no longer import from out/ or out-esbuild in source. TypeScript
and editors resolve ../../../src/common|browser directly. Addon unit test
artifacts bundle those dependencies from source (platform node, npm
packages external).

Reverts preserveConstEnums; const enums are handled in bundled output.

Co-authored-by: Daniel Imms <Tyriar@users.noreply.github.com>

headless/package.json

@@ -3,15 +3,13 @@
  "description": "A headless terminal component that runs in Node.js",
  "version": "6.0.0",
  "main": "lib-headless/xterm-headless.js",
- "module": "lib-headless/xterm-headless.mjs",
+ "module": "lib/xterm.mjs",
  "types": "typings/xterm-headless.d.ts",
- "exports": {
-  "types": "./typings/xterm-headless.d.ts",
-  "import": "./lib-headless/xterm-headless.mjs",
-  "require": "./lib-headless/xterm-headless.js"
- },
  "repository": "https://github.com/xtermjs/xterm.js",
  "license": "MIT",
+ "workspaces": [
+  "addons/*"
+ ],
  "keywords": [
   "cli",
   "command-line",
@@ -27,4 +25,4 @@
   "webgl",
   "xterm"
  ]
-}
+}