Add test/AutoDiff/lit.local.cfg: run tests only when `differentiable_programming`
is enabled in lit. With this, individual tests no longer need
`REQUIRES: differentiable_programming`.
Move multi-functionality SIL tests from test/AutoDiff/SIL/Serialization to
test/AutoDiff/SIL.
Garden test filenames.
The new _Differentiable module is not available in any shipping OS release, but its public API currently doesn’t have availability, either.
Temporarily disable tests that import it when we’re testing with OS-provided libraries.
The typecheck test test/AutoDiff/stdlib/differentiable_protocol.swift imports _Differentable but still somehow succeeds in these configs, so leave that one enabled.
rdar://57975086
Add `Differentiable` conformances for floating-point types to the
`_Differentiation` module. The `TangentVector` associated type for
floating-point types is `Self`.
This design adheres to the differentiable programming manifesto:
docs/DifferentiableProgramming.md.
Partially resolves TF-1052.