Modify/disable built-in snippet

[unional]

vscode: 1.9.0

From discussion: #18963

The copy and override way is not optimal as it creates two identical entries in the list:

It would be better if we can edit or remove the built-in snippet directly.

[jrieken]

We have similar discussions about other non-code extension contributions, like keybindings

[unional]

@jrieken would you consider re-open #18963 also?
The editor.snippetSuggestions: 'top' solution is not good enough.

[jrieken]

dupe of #10565