Changes to environment setup to accommodate new bundle structure

[dehesselle]

Is your feature request related to a problem? Please describe.
In order to modernize the application bundle structure on macOS, the environment setup in crates/rnote-ui/src/env.rs needs to be modified.

Describe the solution you'd like On macOS

• lib_dir needs to return ../Frameworks instead of ../Resources/lib
• GDK_PIXBUF_MODULE_FILE needs to point to ../Resources/etc/loaders.cache

Describe alternatives you've considered
None.

Additional context
I've attached a patch that I've used to check that this works for demonstrational purposes. It needs to be reengineered for GDK_PIXBUF_MODULE_FILE as that shouldn't be set relative to lib_dir. But I don't know Rust and even simple changes give me "you can't do this because it's borrowed..." errors, that's why I cannot submit a PR.

rnote_bundle.patch

[Doublonmousse]

@dehesselle Did you check/use the PR for the mac build on v0.13.1 ?

[dehesselle]

Apologies, I lost track of this. I'll get on this now and report back.

[Doublonmousse]

No worries Thanks for the release !

I figured maybe you pulled the change for the release but didn't report back hence the ping.