Support: clean up comments and Support notation

I tried to get the comments in a similar format, and tried to update the `// Supports` to reflect the current browser reality by testing the bugs out in Browserstack. Those comments were about half with spaces and half without, I took out the spaces but now I think I might want them everywhere instead.

There are only comment changes here, although it reveals at least one chunk of code that could be removed from ajax.js if the comment was correct. That we can do in a separate commit.

In a few places we had redundant `// Supports` comments in both the supports.js and the point where the `support` property was used; several were out of sync. I opted to remove the ones at the point of use and keep them in supports.js for the most part.
I suspect some other rare envs also don't support `gBCR` but don't know which they might be. The critical thing here is that the code will error out without this, whereas now it just gives often-erroneous results in those situations but continues to run and probably works well enough. This workaround doesn't have a lot of size or logic impact so I'm good with leaving it in for now.