Accept editor line height as multiple of font size

[cpsauer]

This PR fixes #115960 with @appetite-j's great suggestion from #105888, also suggested by @usernamehw.
Should also fix #82778.

This is my first PR to VSCode; I'd love your help through!

[ghost]

All CLA requirements met.

[cpsauer]

Tagging @alexdima, in case he's the right reviewer, since he'd been active (and kind) on the issue, and it looks like a lot of the lines in these files are his :)

[cpsauer]

Actually, @alexdima, while you're looking at this:
While making this PR, I'd incidentally noticed that the default line height for macOS has been special-cased to 1.5 rather than the 1.35 for other platforms. (See here.)
This seems odd because Xcode (and thus macOS's) default code multiplier is 1.25, I'm pretty sure. Thoughts on removing that special-casing or to change it to 1.25? Asking you because it looks like you last edited those lines, refactoring from elsewhere. Happy to PR if you agree (and not, if opposed).

[cpsauer]

@alexdima, thanks for the review and making things better!

Looks like your auto-merge got caught by linter download flakiness, so I took a sec to quickly factor the rounding out to be with the minimum constraint. Hope that's okay, since this would have needed a merge from you anyway.

I'd originally had the integer constraint in there, but I noticed that the lines that follow that section break the integer font size constraint, and it looked like things work just fine with non-integer fonts, at least on macOS. Thoughts?

Also hoping I can still get your thoughts on the macOS golden special-casing, above.

[alexdima]

Thank you!

[cpsauer]

Sweet! Thank you, @alexdima.

[cpsauer]

Any chance I could still get your take on the integer & macOS golden sub-questions above?