[vscode] Button in webview title bar not working

[bhufmann]

Bug Description:

Installing the vscode-trace-extension as vsix file (build using PR eclipse-cdt-cloud/vscode-trace-extension#90) in Theia blueprint (based Theia 1.35.0) the open feature doesn't work as expected. The newly added open button in the webview title bar is visible but it seems to be disabled. Installing the same vsix into a Theia application based 1.34.2 it works and the button is enabled and it opens the file dialog. I noticed that when I remove the when clause in the extension definition, then it works as well, however all webviews have that button which is not desired.

Steps to Reproduce:

1. Build the vscode-trace-extension vsix file using PR Add open button in "Open Traces" view eclipse-cdt-cloud/vscode-trace-extension#90 and install it on Theia blueprint based on version 1.35.0
2. Switch to the trace viewer and hover over Opened Traces webview. The open button will appear.
3. Click on button and nothing happens.

The following video shows the successful case:
221713381-b9f81799-939a-4065-9966-2e7ade116c3e.webm

Additional Information

• Operating System: Linux Ubuntu 20.04
• Theia Version: 1.35.0

[msujew]

Possibly related to #12182.

[vince-fugnitto]

Possibly related to #12182.

@msujew it seems to be broken with 81b98d6, same with other toolbar items (ex: vscode.git that Alvaro was testing in #12295).

[alvsan09]

As mentioned above, a related issue can be observed when testing #12295,

Using the vscode.git builtin extension (see PR's test instructions).
When a commit is triggered via the inline tab-bar menu, an editor for the file COMMIT_EDITMSG will appear containing two tab-bar contributions to 'Accept' or 'Discard'.
Since the icons are visible it's clear that the 'when' conditions passed, but when the buttons are pressed, no action takes place i.e. the 'when' condition no longer pass.
There seems to be a problem with the resolution of the related monaco context.