[6.0] [AST] Change some builtins to conform their result to Escapable

[Azoy]

This is a cherry pick of #72594 to help future conflicts/dependent PRs be able to build and test using the new ~Escapable feature.

• Scope: Broadens some internal builtins to accept/return escapable types in their function signatures. This should only affect the standard library modules as they are generally the only ones supposed to be using Builtin.
• Main Branch PR: [AST] Change some builtins to conform their result to Escapable #72594
• Risk: Very Low
• Reviewed By: @atrick @meg-gupta
• Testing: Not needed

[Azoy]

@swift-ci please test

[tbkka]

Caveat: The ~Escapable feature looks likely to remain experimental for 6.0, and thus only available with an experimental-feature flag. It doesn't look like anything here needs to be feature-gated, but keep in mind that the surface syntax won't be universally available for a while longer.