Use new built-in telemetry masking

[bwateratmsft]

The @vscode/extension-telemetry package recently added support for custom masking. (Note: At the time of writing it has not yet been released.)

We should investigate using this instead of our current more ad-hoc masking logic. One limitation is that it doesn't support adding masks after-the-fact, so we would need to see if it's possible to change all of our masks to more generic, statically-defined regexs.

[bwateratmsft]

Related to #1360 as well