Extend context.rs to dynamically find the OUT_DIR for certain assets

[sinistersnare]

Hello, my team is moving to Bazel, and we can not use tauri-cli or any of your custom cargo-based tooling. We would like to contribute our changes to you all, so you can better support Bazel.

These changes should be non-breaking, as it just recalculates the OUT_DIR at build.rs-time and compile-time separately. So it should not affect Cargo builds.

I think that TODO, if this is going to be fully generalized we need to add this functionality to some other parts of at least this file.

What kind of change does this PR introduce?

• Bugfix
• Feature
• Docs
• New Binding issue #___
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change?

• Yes, and the changes were approved in issue #___
• No

Checklist

• When resolving issues, they are referenced in the PR's title (e.g fix: remove a typo, closes #___, #___)
• A change file is added if any packages will require a version bump due to this PR per the instructions in the readme.
• I have added a convincing reason for adding this feature, if necessary

Other information

[lucasfernog]

@sinistersnare is this PR ready or do you want to change some other OUT_DIR usage?

[sinistersnare]

I think its fine for now. It can be further extended as needed using the code here as a template for future contributors.

[lucasfernog]

By the way @sinistersnare this PR is targeting v2. So if you want this to be part of v1.5, it needs to target the 1.x branch instead.

[sinistersnare]

Ah thanks for the check on that. I rebased on 1.x

[sinistersnare]

I extended the PR to include another case useful to my project. Overall, this kind of stuff is really useful for non-Cargo users, and the codegen crate would be wise to generalize from any build tool.