Refactor typed om implementation

[johannesodland]

Moving the internal implementation of typed om into its own folder.
CSSNumericValue and subclasses are split into separate files.

[bramus]

I’d also move src/proxy-cssom.js into that folder to contain all CSSOM related polyfilling into that folder. I think it would also make sense to out the several classes into their own separate files. This is something I also considered doing in #221.

[johannesodland]

Yeah.. That makes sense. I didn't realize #221 was merged.

I've moved src/proxy-cssom.js also now.

Do you want me to split out some of the classes, or should we do that in a separate PR?

[bramus]

It can go in this PR, as it's all about reorganization.

[johannesodland]

Moved the token classes into a separate file now, when it comes to the CSSNumericValue classes, I think they should stay in proxy-cssom?

[bramus]

Yes. That way, eventually, the whole cssom block can graduate to being its own package.

[bramus]

Re-reading my comment I wasn't clear here. I interpreted "staying in CCSOM" as stay in the folder.

What I mean is: I'd split off these classes into their own files, one class per file.

[johannesodland]

Got it :)

I split the classes into their own files and switched from using a WeakMap for the internals to using private class fields.