rust data loader example

[nthiad]

Changelog

Adds rust data loader example.

Docs

None

Description

This PR adds a rust data loader example with the example file from the foxglove_data_loader in foxglove-sdk/#460 plus the typescript build to generate the extension.

The example in the sdk repo is rust-only to keep that repo simpler and so that users can understand only that rust code in isolation, but the example here in create-foxglove-extension is more complete and something we can point people to for everything they will need to make an extension of their own.

Replaces #169.

Fixes: FG-11789

Depends on foxglove/foxglove-sdk#460

[linear]

FG-11789 create-foxglove-extension support for data loaders

[nthiad]

CI is failling due to https://linear.app/foxglove/issue/FG-12000/creating-a-new-foxglove-extension-with-2290-is-broken-due-to-missing

[defunctzombie]

Should we set this to a specific commit so that if we iterate on the api the example remains valid until we explicitly update it?

[nthiad]

that could work so long as the WIT interface upstream in app doesn't change very often

[nthiad]

Upstream in foxglove_data_loader I added init.get_channel() and updated this example to pass the init object down to the iterator. Now the init object can manage the mappings based on topics, which I feel is much nicer than adding a struct field in the data loader and message iterator for each channel to save its id.

let init = self.init.borrow();
let acc_ch_id = init.get_channel("/accelerometer").unwrap().id;
let temp_ch_id = init.get_channel("/temperature").unwrap().id;

[nthiad]

Now the trait interface methods are &mut self so I was able to remove the RefCells so we don't have to explain those to users.