[stdlib] Optional: Allow non-escapable wrapped types

[lorentey]

This quick experimental PR generalizes Optional to support non-escapable payloads, itself becoming conditionally escapable.

rdar://125927256

[lorentey]

@swift-ci test

[Azoy]

Can we get the ExpressibleByNilLiteral and init(_ wrapped: consuming Wrapped) initializer supported?

[lorentey]

For ExpressibleByNilLiteral, I believe we still need to figure out how to express indefinite lifetime for the result of the init(nilLiteral:) initializer.

[lorentey]

@swift-ci test

[lorentey]

@swift-ci test

[lorentey]

@swift-ci test

[lorentey]

@swift-ci build toolchain

[lorentey]

The last push added generalizations for MemoryLayout, ExpressibleByNilLiteral and unsafeBitCast in addition to a somewhat working Optional generalization.

I had to temporarily disable module verification and silence a bogus diagnostic to make this stuff work. Hopefully that'll go away soon.

[lorentey]

@swift-ci test

[lorentey]

@swift-ci build toolchain

[lorentey]

@swift-ci test

[lorentey]

@swift-ci build toolchain

[lorentey]

@swift-ci test

[lorentey]

@swift-ci build toolchain

[lorentey]

@swift-ci build toolchain

[glessard]

@swift-ci please build toolchain

[glessard]

@swift-ci smoke test

[lorentey]

@swift-ci test

[lorentey]

@swift-ci build toolchain