Add support for xcodebuild file formats

[petamas]

This PR adds support for various xcodebuild related file formats.

I've modeled this change based on the pre-existing MSBuild formats. For every new extension:

• If it is a non-plist format, it gets the text tag. (plists are put in the EXTENSIONS_NEED_BINARY_CHECK dictionary without a text tag.)
• If the format is implemented as a known format (JSON/XML/plist), it gets the appropriate tag.
• It gets its own tag, same as the extension.
• It gets an xcodebuild tag to group all of them, similarly as the msbuild tag.

I've applied the same tagging logic to the pre-existing xctestplan format. (I.e. I added the xcodebuild tag to it.)

Unfortunately, I did not find direct sources from Apple's documentation about the internals of all the formats, but I've verified each of them based on examples and third-party blogposts.