Move compiler crates to crates directory

As part of #451, we want to clean up our workspace a bit, and a big step towards improving the current state of things, is to move all of the compiler implementation crates into a `crates/` directory in the project root. This would leave the root directory for global configuration, and high-level sub-projects of the compiler (e.g. integration tests, SDK, cargo-miden).

I'm aiming for more or less this:

```
compiler
|- crates
| |- codegen
| |- debug
| |- dialects
| |- eval
| |- frontend
| |- hir
| |- analysis
| |- macros
| |- symbol
| |- transform
| |- type
| |- compile
| |- driver
| |- session
|
|- docs
|
|- examples
|
|- sdk
|
|- tests
|
|- tools
| |- cargo-miden
| |- midenc
```