Make texture=, shader= setters work on Weak* types

[planetis-m]

Somehow tmp are not sinked into the setter and a destructor call is generated in the outer scope.

[planetis-m]

Right that was done on purpose in order to be able to share resources, however this design hits a limit with temporaries. the fix isn't obvious.

[planetis-m]

It actually makes sense for these setters to only accept Weak* counterparts making it explicit that they are unmanaged resources.

[planetis-m]

On the other hand, it's not a weak resource, UnloadMaterial unloads both shader and all the textures... But if part of a Model, then it's not destroyed...

[planetis-m]

I am going full circle here, that's what the repo used in 88cd872 that's a year ago!

[planetis-m]

Also review getShapesTexture and getFontDefault.

[planetis-m]

The solution here is to make a setter with parameter constraints that disallow rvalues.