[AutoDiff upstream] Serialize derivative function configurations. (#30672)

Serialize derivative function configurations per module.

`@differentiable` and `@derivative` attributes register derivatives for
`AbstractFunctionDecl`s for a particular "derivative function configuration":
parameter indices and dervative generic signature.

To find `@derivative` functions registered in other Swift modules, derivative
function configurations must be serialized per module. When configurations for
a `AbstractFunctionDecl` are requested, all configurations from imported
modules are deserialized. This module serialization technique has precedent: it
is used for protocol conformances (e.g. extension declarations for a nominal
type) and Obj-C members for a class type.

Add `AbstractFunctionDecl::getDerivativeFunctionConfigurations` entry point
for accessing derivative function configurations.

In the differentiation transform: use
`AbstractFunctionDecl::getDerivativeFunctionConfigurations` to implement
`findMinimalDerivativeConfiguration` for canonical derivative function
configuration lookup, replacing `getMinimalASTDifferentiableAttr`.

Resolves TF-1100.

lib/Serialization/SerializedModuleLoader.cpp

@@ -993,6 +993,17 @@ void SerializedModuleLoaderBase::loadObjCMethods(
   }
 }
 
+void SerializedModuleLoaderBase::loadDerivativeFunctionConfigurations(
+    AbstractFunctionDecl *originalAFD, unsigned int previousGeneration,
+    llvm::SetVector<AutoDiffConfig> &results) {
+  for (auto &modulePair : LoadedModuleFiles) {
+    if (modulePair.second <= previousGeneration)
+      continue;
+    modulePair.first->loadDerivativeFunctionConfigurations(originalAFD,
+                                                           results);
+  }
+}
+
 std::error_code MemoryBufferSerializedModuleLoader::findModuleFilesInDirectory(
     AccessPathElem ModuleID,
     const SerializedModuleBaseName &BaseName,