Fixes the following Clang 7 warnings:
```
core/io/marshalls.cpp:872:10: warning: unused variable 'f' [-Wunused-variable]
core/ustring.cpp:1831:2: warning: 'register' storage class specifier is deprecated and incompatible with C++17 [-Wdeprecated-register]
core/ustring.cpp:1832:2: warning: 'register' storage class specifier is deprecated and incompatible with C++17 [-Wdeprecated-register]
drivers/gles3/rasterizer_gles3.cpp:82:24: warning: unused function '_gl_debug_print' [-Wunused-function,34]
main/main.cpp:118:13: warning: unused variable 'auto_build_solutions' [-Wunused-variable]
modules/csg/csg_gizmos.cpp:225:46: warning: 'current' may be used uninitialized in this function [-Wmaybe-uninitialized]
```
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.
-Missing Icons
-Missing freezing option (for baking light and faster load)
-Missing a way to export from Godot (GLTF2?)
-Probably buggy (may freeze editor, can be worked around easily, but let me know if this happens so it's easier to catch bugs)
Happy testing!
