NSURL dataRepresentation inits should allow some invalid URLs the old parser accepted

[jrflat]

Fix Swift CFURL parsing to accept some invalid URL strings that the old parser accepted for data representation inits.

Motivation:

CFURLCreateWithBytes and CFURLCreateAbsoluteURLWithBytes generally accept any input and percent-encode it until it's valid. However, the new Swift code path for these functions rejected some invalid URL formats. This caused +[NSURL (absolute)URLWithDataRepresentation:] to return nil for data that previously succeeded, such as IP-literal hosts with invalid characters, unterminated [ brackets, and relative paths with : in the first segment.

Modifications:

• Gate the strict IP-literal content, unterminated [, and colon-in-relative-path rejection on useModernParsing: true, so the CFURL byte encoding path is as lenient as the old parser.
• When encoding an invalid IP-literal for CFURL, preserve the [ and ] bracket delimiters and only percent-encode the inner content.
• Use span.extracting(_:) more often for safer index validation.

Result:

Data representation inits accept the same URL strings as the old parser.

Testing:

Added unit tests for data representation NSURLs with invalid IP-literals, unterminated brackets, spaces in hosts, and relative paths with colons.

[jrflat]

@swift-ci please test

[jrflat]

@swift-ci please test Windows Platform

[jrflat]

@swift-ci please test

[jrflat]

@swift-ci please test