Uplevel xterm.js

This brings in:

- UIEvent.detail usage
- Search addon refactor

Fixes #20505

npm-shrinkwrap.json

@@ -442,7 +442,7 @@
     "xterm": {
       "version": "2.8.0",
       "from": "Tyriar/xterm.js#vscode-release/1.15",
-      "resolved": "git+https://github.com/Tyriar/xterm.js.git#81204d4ff2e80b4d1fb89e5e4c2cd436124193b3"
+      "resolved": "git+https://github.com/Tyriar/xterm.js.git#90df2bcb7caa712e0a12591798c3e535a9d607cd"
     },
     "yauzl": {
       "version": "2.3.1",

src/vs/workbench/parts/terminal/electron-browser/terminalInstance.ts

@@ -39,6 +39,9 @@ import pkg from 'vs/platform/node/package';
 /** The amount of time to consider terminal errors to be related to the launch */
 const LAUNCHING_DURATION = 500;
 
+// Enable search functionality in xterm.js instance
+(<any>xterm).loadAddon('search');
+
 class StandardTerminalProcessFactory implements ITerminalProcessFactory {
 	public create(env: { [key: string]: string }): cp.ChildProcess {
 		return cp.fork('./terminalProcess', [], {