Reduce unnecessary COW on Vector by make writing explicit

This commit makes operator[] on Vector const and adds a write proxy to it.  From
now on writes to Vectors need to happen through the .write proxy. So for
instance:

Vector<int> vec;
vec.push_back(10);
std::cout << vec[0] << std::endl;
vec.write[0] = 20;

Failing to use the .write proxy will cause a compilation error.

In addition COWable datatypes can now embed a CowData pointer to their data.
This means that String, CharString, and VMap no longer use or derive from
Vector.

_ALWAYS_INLINE_ and _FORCE_INLINE_ are now equivalent for debug and non-debug
builds. This is a lot faster for Vector in the editor and while running tests.
The reason why this difference used to exist is because force-inlined methods
used to give a bad debugging experience. After extensive testing with modern
compilers this is no longer the case.

drivers/wasapi/audio_driver_wasapi.cpp

@@ -447,7 +447,7 @@ void AudioDriverWASAPI::thread_func(void *p_udata) {
 			ad->audio_server_process(ad->buffer_frames, ad->samples_in.ptrw());
 		} else {
 			for (unsigned int i = 0; i < ad->buffer_size; i++) {
-				ad->samples_in[i] = 0;
+				ad->samples_in.write[i] = 0;
 			}
 		}