Add MakeVerifiedLocIdAndInst for runtime validation (#6942)

This follows up on a discussion about wanting to use `Any*` inst
clusters to handle boilerplate construction, with the issue that
`UncheckedLoc` use removes validation. Some context is at
https://github.com/carbon-language/carbon-lang/pull/6930#discussion_r2963157428.

This folds in `MakeImportedLocIdAndInst` because the logic is related,
particularly for `LocId` values which are `ImportIRInstId`, and it
eliminates questions of what the right function is to use.

This uncovers an error in the `NodeKind` associated with
`FormBindingPattern`. For now I'm just adding a TODO regarding that.

Assisted-by: Google Antigravity with Gemini

toolchain/check/function.cpp

@@ -454,7 +454,8 @@ auto MakeFunctionDecl(Context& context, SemIR::LocId loc_id,
   SemIR::FunctionDecl function_decl = {SemIR::TypeId::None,
                                        SemIR::FunctionId::None, decl_block_id};
   auto decl_id = AddPlaceholderInstInNoBlock(
-      context, SemIR::LocIdAndInst::UncheckedLoc(loc_id, function_decl));
+      context, SemIR::LocIdAndInst::RuntimeVerified(context.sem_ir(), loc_id,
+                                                    function_decl));
   function.first_owning_decl_id = decl_id;
   if (is_definition) {
     function.definition_id = decl_id;