Uplevel xterm.js

This adds the fix for #18370 which was cherry picked to the Tyriar/xterm
vscode-release/1.9 branch (as it's in review).

Fixes #18370

npm-shrinkwrap.json

@@ -432,7 +432,7 @@
     "xterm": {
       "version": "2.2.3",
       "from": "git+https://github.com/Tyriar/xterm.js.git#vscode-release/1.9",
-      "resolved": "git+https://github.com/Tyriar/xterm.js.git#67eaa7ee4a7a028acc6ef88b01e800c24d534875"
+      "resolved": "git+https://github.com/Tyriar/xterm.js.git#7fcf6d1bcdaa0df9905673251f5f9336798932e5"
     },
     "yauzl": {
       "version": "2.3.1",