Go's stdlid now has a maps package, which is very useful. We have been using imports on the form `xmaps "maps"`, but auto import tools doesn't handle this, which is annoying.
I have been thinking about this for some time, but have been holding back because of all the import changes. However, now is a good time to do this, with very little unmerged code.
Instead of maintaing a list of all CSS units and functions this commit:
* Uses 3 regexps to detect typed CSS values (e.g. `24px`) + properly handle numeric Go types.
* These regexps may have some false positives -- e.g. strings that needs to be quoted.
* For that rare case, you can mark the string with e.g. `"32xxx" | css.Quoted`
* For the opposite case: `"32" | css.Unquoted`
Updates #10632
Bjørn Erik Pedersen