Use try syntax for Option where appropriate
- [x] `./mach build -d` does not report any errors
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Implement GetAvailability for Bluetooth
<!-- Please describe your changes on the following line: -->
This implements the [getAvailability](https://webbluetoothcg.github.io/web-bluetooth/#dom-bluetooth-getavailability) function from the spec.
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- [ ] These changes fix #__ (github issue number if applicable).
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Remove the util crate
<!-- Please describe your changes on the following line: -->
This PR removes the `util` crate.
* Replaced the `spawn_named` and `clamp` functions by appropriate uses of `std:🧵:Builder::spawn`, `std::cmp::min` and `std::cmp::max`.
* Moved `opts`, `prefs` and `resource_files` into a new `config` crate.
* Moved `remutex` and `geometry` into their own crates.
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Check if represented attributes are cached
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Improve existing cache checks in `/bluetooth/lib.rs`, and update Step comments in `script/dom` corresponding to this.
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Add Start/Stop notifications
Add support for Start and Stop Notifications for WebBluetooth
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- [X] There are tests for these changes
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