[AutoDiff upstream] define autodiff builtins

[marcrasi]

Defines type signatures and SILGen for the following builtins:

/// Applies the {jvp|vjp} of `f` to `arg1`, ..., `argN`.
func applyDerivative_arityN_{jvp|vjp}(f, arg1, ..., argN) -> jvp/vjp return type

/// Applies the transpose of `f` to `arg`.
func applyTranspose_arityN(f, arg) -> transpose return type

/// Makes a differentiable function from the given `original`, `jvp`, and `vjp` functions.
func differentiableFunction_arityN(original, jvp, vjp)

/// Makes a linear function from the given `original` and `transpose` functions.
func linearFunction_arityN(original, transpose)

Includes a SILGen filecheck test for all of these.

[marcrasi]

@swift-ci please smoke test

[dan-zheng]

Merging to unblock progress.