[Firestore] Programmatically link un-linked symbols (#10896)

* [Firestore] Force link un-linked symbols

* Style

Author: ncooke3

Firestore/Source/API/FIRFirestore.mm

@@ -545,6 +545,17 @@ - (void)terminateInternalWithCompletion:(nullable void (^)(NSError *_Nullable er
   _firestore->Terminate(MakeCallback(completion));
 }
 
+#pragma mark - Force Link Unreferenced Symbols
+
+extern void FSTIncludeFSTFirestoreComponent(void);
+
+/// This method forces the linker to include all the Analytics categories without requiring app
+/// developers to include the '-ObjC' linker flag in their projects. DO NOT CALL THIS METHOD.
++ (void)notCalled {
+  NSAssert(NO, @"+notCalled should never be called");
+  FSTIncludeFSTFirestoreComponent();
+}
+
 @end
 
 NS_ASSUME_NONNULL_END

Firestore/Source/API/FSTFirestoreComponent.mm

@@ -176,4 +176,9 @@ + (void)load {
 
 @end
 
+/// This function forces the linker to include `FSTFirestoreComponent`. See `+[FIRFirestore
+/// notCalled]`.
+void FSTIncludeFSTFirestoreComponent(void) {
+}
+
 NS_ASSUME_NONNULL_END