Make ContiguousBytes refine ~Copyable & ~Escapable and add Span family conformances

[jmschonfeld]

Now that downstream issues have been resolved, this updates ContiguousBytes to refine ~Copyable and ~Escapable and adds conformances for the span family of types

Motivation:

This implements some of the API changes proposed in SF-0034 to allow ContiguousBytes-based APIs to accept spans by adding ~Copyable and ~Escapable refinements to those APIs.

Modifications:

• Add ~Copyable and ~Escapable refinements to ContiguousBytes
• Add conformances for the span family of types to ContiguousBytes

Result:

Spans conform to ContiguousBytes and can be passed to APIs that accept a ContiguousBytes & ~Escapable & ~Copyable

Testing:

Covered by existing unit tests of ContiguousBytes

[jmschonfeld]

@swift-ci please test