Auto merge of #20578 - kwonoj:refactor-bluetooth-manager, r=paulrouget

refactor(bluetooth): removes direct ui invocation from bluetooth thread

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Relates to #20429.

This PR is mostly blocked by https://github.com/servo/servo/pull/20480, cause both are nearly identical change in crux and based on review of prior changes this PR need to be updated. Just didn't want assigned issue hanging without visible progresses, so prepped PR to followup further.

(mostly copy-paste from pair PR)

Probably point of review / need to be updated are

1. Communication between components
Currently it's wired as like below:
```
+----------------+                    +---------------+              +---------+
|                |  constellationMsg  |               | embedderMsg  |         |
| bluetooth_thread +----------------->+ constellation +------------->+ browser |
|                |                    |               |              |         |
+-----+----------+                    +---------------+              +----+----+
      ^                                                                   |
      +-------------------------------------------------------------------+
                                device: String
```
- is this feasible approach?
- does organization of message / fn (where to put consteallation / embedder msg & fns) are legit?

2. Invoking tfd in a separate thread
- This was mainly to align behavior to previous implentation, where tfd was invoked inside of filemanager_thread so does not block main. It may possibly just let block instead.

and of course, a lot of other codes need to follow better practices.

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- [ ] `./mach build-geckolib` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #20429 (github issue number if applicable).

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