terminal: update xterm-addon-webgl to fix rendering issues

The xterm-addon-webgl addon is built from my github repo [1] and
uploaded to our gs bucket. I am getting my fixes into the upstream so
that we don't need to do this any more.

[1] https://github.com/JasonXJ/xterm.js/commit/f233f02f12ebb7dbd53502e5a4fafec1e55f781f

Bug: b/236205389
Change-Id: I82b1b8f2c1d685026dab0c2246586742007f67da
Reviewed-on: https://chromium-review.googlesource.com/c/apps/libapps/+/3878153
Reviewed-by: Joel Hockey <joelhockey@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>
diff --git a/terminal/js/terminal_emulator.js b/terminal/js/terminal_emulator.js
index a3e7c31..35c3243 100644
--- a/terminal/js/terminal_emulator.js
+++ b/terminal/js/terminal_emulator.js
@@ -160,7 +160,7 @@
     this.enableWebGL_ = enableWebGL;
 
     // TODO: we should probably pass the initial prefs to the ctor.
-    this.term = testParams?.term || new Terminal();
+    this.term = testParams?.term || new Terminal({allowProposedApi: true});
     this.fontManager_ = testParams?.fontManager || fontManager;
 
     /** @type {?Element} */