Allow square brackets in Swift CFURL path, query, and fragment

[jrflat]

Allow "[" and "]" to exist unencoded in the path, query, and fragment of CFURL.

Motivation:

The old CFURL implementation allowed "[" and "]" anywhere in the URL string due to a quirk of how IPv6 literals were implemented (despite both RFC 3986 and the old RFC 1808 only allowing those characters in the host component). We should match this behavior for the path, query, and fragment components for compatibility with both the old implementation and the WHATWG URL spec as a bonus.

Modifications:

• Allow "[" and "]" unencoded in the path, query, and fragment components
• Update the addPercentEscapes function used during string encoding to use the newer, faster URLComponentAllowedSet implementation, which I forgot to do earlier. The older URLComponentAllowedMask bitmasks used by URLComponents and the CFURL/NSURL file path initializers still behave the same as before and as expected for those APIs. We can investigate allowing "[" and "]" for those separately.

Result:

CFURL again allows "[" and "]" in path, query, and fragment components and does not return NULL.

Testing:

CFURL/NSURL unit test with the Swift implementation enabled.

[chloe-yeo]

Looks good to me!

[jrflat]

@swift-ci please test

[itingliu]

It looks like this codepath is available everywhere, not just behind #if FOUNDATION_FRAMEWORK? If so would it be possible to add a test for this change even though there's no public Swift URL API that exercises this path?

[jrflat]

It looks like this codepath is available everywhere, not just behind #if FOUNDATION_FRAMEWORK? If so would it be possible to add a test for this change even though there's no public Swift URL API that exercises this path?

Sure the internal function should be testable, I can add a test

[jrflat]

@swift-ci please test