Unit tests should catch unexpected jumps in file sizes in VSIX

We have unit tests (`PackageContentTests`?) that validate the set of files in the VSIX files we build. These only catch if files are unexpectedly removed or added.

We should also have a test that fails if the size of included files jumps unexpectedly. It might also be helpful to check if file sizes _drop_ unexpectedly too.

We would have to baseline the expected file sizes in the tests themselves. On occasion we would need to update these baselines due to product evolution.