Fix errors with latest @babel/generator

[dfreeman]

A few separate but related issues have popped up as our upstream dependencies (specifically the Babel-related ones) have evolved lately:

• Browserslist gets cranky when it's not on a recent enough version. We don't actually care because we aren't doing transpilation for real targets, but Babel ends up implicitly loading it on startup, which can trigger the warning. Accordingly, we disable the warning in the entrypoint to the language server and CLI executables.
• babel/babel#14113 made generate(someTSTypeParameterDeclarationNode) throw, as it now cares about details of its parent node. Babel should maybe handle that more gracefully, but it's trivial for us to work around by generating code for the declarations individually rather than altogether.

The Browserslist issue was a ticking timebomb we would have hit eventually regardless, but a few different consumers ran into the @babel/generator just from refreshing other random dependencies and happening to get a Babel update. To help get ahead of that situation in the future, I'm also adding a floating dependencies scenario to our CI config.