Enable `@differentiable` attribute on setters of properties and
subscripts in `Differentiable`-conforming types.
Add automatically-differentiated `@differentiable` setter test.
Resolves TF-1166.
Fix SIL differential function type calculation to handle non-wrt `inout`
parameters.
Patch `SILFunctionType::getDifferentiabilityResultIndices` to prevent returning
empty result indices for `@differentiable` function types with no formal results
where all `inout` parameters are `@noDerivative`. TF-1305 tracks a robust fix.
Resolves SR-13305.
Exposes TF-1305: parameter/result differentiability hole for `inout` parameters.
