Desktop: Make embedded resources optional

[timon-schelling]

• Why: Multiple devs where confused/annoyed by an error that came from a missing frontend dist dir.
• Add a embedded_resources feature
• Add a build script that sets cfg(embedded_resources) if resource dir exists
• Emits warning when resource dir doesn't exist
• embedded_resources are in a separate crate
  • reduces parse times for the desktop crate (dir is included as byte string, about 10 sec extra build time)
  • makes it very clear what the build script is used for
  • no build script in desktop
• allows specifying GRAPHITE_RESOURCES when build without the embedded_resources feature
• preparation for watch command for desktop
• Cleans resource handler code (moved to cef internal module etc.)

[Keavon]

I'm unfamiliar with what kinds of resources these are, could you give some examples please?

[timon-schelling]

I'm unfamiliar with what kinds of resources these are, could you give some examples please?

The frontend files, frontend/dist.

[TrueDoctor]

Would it make sense to make this a Cow<'static, [u8]> ?

[timon-schelling]

The results of a fs::read cannot be 'static, see usage of this struct.

[timon-schelling]

if let Ok(data) = std::fs::read(file_path) {
    return Some(Resource { data, mimetype });
}

[TrueDoctor]

Yes, but include dir should give you static references, right?

[timon-schelling]

Yes, but this pr also adds the ability to create resources from disk. Could be behind feature flag for now, but would like to have override functionality in the future.