platformName/browserName case sensitivity

Currently platformName/browserName have to be passed in ASCII lowercase to match (they're lowercased before comparison); some quick testing makes it seem like chromedriver and geckodriver do have this behaviour, but safaridriver does not.

Searching on GitHub suggests there's a reasonably large amount of usage, of "Android" and "iOS" especially (and the latter makes me wonder if chromedriver and/or geckodriver do something different for Android?). That said, even Windows, Linux, macOS see common usage — even on the Selenium docs (cc @shs96c). That said, I wonder if Selenium is lowercasing them before it gets beyond it?

I'm slightly hesitant about changing behaviour of iOS here, but probably needs more testing to check what various implementations do when given an uppercase platformName/browserName — does it simply never reach the wire protocol?

Start with the linked WebDriver specification sections on ASCII lowercasing and capability matching, then compare uppercase platformName and browserName behavior across the referenced drivers. Record whether the behavior is consistent and determine whether the specification needs a clarified requirement or no change.