Downgrade VS Code Compatibility version to 1.66

[JonasHelming]

As discussed in the Theia Dev Call on Jan 24th:

We will downgrade the VS Code compatibility version from 1.68 to 1.66 for now. 1.68 only adds the Tab related APIs. Theia currently only stubs this API.
The real implementations is about to be finished, but wont make it to the release.
As the stub for the tab API can produce unexpected behavior for users, we decided set compatibility back to 1.66 meaning that extensions using the tab API are not officially supported in the next release. We will upgrade the version again once the real implementation is done.

Adopters can change the compatibility to 1.68 if they wish for. The tab API is stubbed. Calls to the tab API might produce unexpected results. However, if the tab API is not used, changing to 1.68 will allow to install more extensions

See also: #12104

[JonasHelming]

We will backport the implementation of the tab API to the community release stream once it is available

[JonasHelming]

#12109 is now available (@vince-fugnitto @colin-grant-work @tsmaeder)

[JonasHelming]

Ses #12140