Removed all `#![feature]` flags, except for `#![feature(test)]`. Once parser benchmarks are ported to something that is compatible with stable rust, we will be able to switch to it.
# Important Notes
The command to run the gui dev environment has been changed. Invoking the old command will print a message about that.
From now on, use `pnpm dev:gui2` in repository root.
- Remove unnecessary modules
- Remove `ts-plugin-namespace-auto-import` as it was a workaround to use the non-conventional `import *` convention
- Remove `esbuild-plugin-copy-directories` as it is unuse
- Inline modules that are only ever used once
- Inline `project-manager-shim` into `gui2` - it is only used during `gui2`'s dev mode
- Inline `content-config` into `client`
- Flatten `app/ide-desktop/lib/` to `app/ide-desktop/`
- Flatten `app/ide-desktop/lib/dashboard/` to `app/dashboard/`
# Important Notes
- As mentioned above, all remaining modules have been moved up from `app/ide-desktop/lib/` to `app/ide-desktop/`. It's not ideal but I'd rather hold off on moving them anywhere else before we have a consensus on what should go where.
- (That is to say, this may not be the final directory structure - but I figure it's fine to get *something* done so that hopefully the rest of the restructuring is simpler.)
