Allow identifying assets in code from their path

[RiscadoA]

Problem

Currently assets are only identified by their UUID. This is great for automated tools and stuff, where human eyes are not needed. But when a dev wants to refer to an asset and needs to manually identify it, be it in scene asset files, or in code, its not readable at all, nor fun, to have to store an UUID there.

Solution

We should also allow assets to be identified by their path. For example, instead of:

static const Asset<Scene> RedCubeSceneAsset = AnyAsset("1aa5e234-28cb-4386-99b4-39386b0fc221");

We could write:

static const Asset<Scene> RedCubeSceneAsset = AnyAsset("/assets/scenes/red_cube.cubos");

This should be a matter of:

• storing an extra string jn AnyAsset, empty by default;
• on Assets, on all methods that receive handles, handles with non empty path strings should be translated to handles with UUIDs.