Reflection: type aliases

## What problem does this solve or what need does it fill?

The ability to define reflection type names that are both stable and reasonably succinct would be valuable, particularly in cases involving evolution of asset formats:

## What solution would you like?

From the discord:
```
#[reflect(Reflect)]
#[type_path(alias = scenery::FloorSurface)]
struct StdFloorSurface { .. }
```
## Additional context

There's a PR #5830 which attempts to solve this problem in a slightly different way.

Start by reviewing the reflected type example in the issue and PR #5830, which attempts a related solution. Compare the proposed alias syntax with the existing reflection and asset-format evolution needs. Done means reaching an agreed design for stable, succinct reflection type names and implementing it consistently.

Written by the indexing model from the issue text.