[SR-14339] UUID should conform to ContiguousBytes

[belkadan]

Previous ID	SR-14339
Radar	rdar://problem/75364846
Original Reporter	@belkadan
Type	Improvement

Additional Detail from JIRA

Votes	0
Component/s	Foundation
Labels	Improvement
Assignee	None
Priority	Medium

md5: c7a8f847a64129ff30490a24e1e22e74

Issue Description:

A UUID has a fixed byte-based representation (uuid_t); it would be nice™ to expose that through ContiguousBytes in addition to the uuid property.

[belkadan]

Probably blocked on figuring out backwards-deployable conformances / conformances with availability, though.

[typesanitizer]

@swift-ci create