[AutoDiff] Disable differentiable_function_extract explicit type as… (#35239)

`differentiability_function_extract` instruction has an optional explicit
extractee type. This is currently used by TypeSubstCloner and the
LoadableByAddress transform to rewrite `differentiability_function_extract`
instructions while preserving `@differentiable` function type invariants.

There is an assertion that `differentiability_function_extract` instructions do
not have explicit extractee types outside of canonical/lowered SIL. However,
this does not handle the SIL deserialization case above: when a function
containing a `differentiable_function_extract` instruction with an explicit type
is deserialized into a raw SIL module (which happens when optimizations are
enabled).

Removing the assertion unblocks this encountered use case.

A more robust longer-term solution may be to change SIL `@differentiable`
function types to explicitly store component original/JVP/VJP function types.

Also fix `differentiable_function_extract` extractee type serialization.

Resolves SR-14004.

lib/SIL/IR/SILInstructions.cpp

@@ -731,18 +731,6 @@ DifferentiableFunctionExtractInst::DifferentiableFunctionExtractInst(
                                : getExtracteeType(function, extractee, module),
                            function.getOwnershipKind()),
       Extractee(extractee), HasExplicitExtracteeType(extracteeType.hasValue()) {
-#ifndef NDEBUG
-  if (extracteeType.hasValue()) {
-    // Note: explicit extractee type is used to avoid inconsistent typing in:
-    // - Canonical SIL, due to generic specialization.
-    // - Lowered SIL, due to LoadableByAddress.
-    // See `TypeSubstCloner::visitDifferentiableFunctionExtractInst` for an
-    // explanation of how explicit extractee type is used.
-    assert((module.getStage() == SILStage::Canonical ||
-            module.getStage() == SILStage::Lowered) &&
-           "Explicit type is valid only in canonical or lowered SIL");
-  }
-#endif
 }
 
 SILType LinearFunctionExtractInst::