Add a command for building and installing a locally-developed Zed extension (#8781)

This PR adds an `zed: Install Local Extension` action, which lets you
select a path to a folder containing a Zed extension, and install that .
When you select a directory, the extension will be compiled (both the
Tree-sitter grammars and the Rust code for the extension itself) and
installed as a Zed extension, using a symlink.

### Details

A few dependencies are needed to build an extension:
* The Rust `wasm32-wasi` target. This is automatically installed if
needed via `rustup`.
* A wasi-preview1 adapter WASM module, for building WASM components with
Rust. This is automatically downloaded if needed from a `wasmtime`
GitHub release
* For building Tree-sitter parsers, a distribution of `wasi-sdk`. This
is automatically downloaded if needed from a `wasi-sdk` GitHub release.

The downloaded artifacts are cached in a support directory called
`Zed/extensions/build`.

### Tasks

UX

* [x] Show local extensions in the Extensions view
* [x] Provide a button for recompiling a linked extension
* [x] Make this action discoverable by adding a button for it on the
Extensions view
* [ ] Surface errors (don't just write them to the Zed log)

Packaging

* [ ] Create a separate executable that performs the extension
compilation. We'll switch the packaging system in our
[extensions](https://github.com/zed-industries/extensions) repo to use
this binary, so that there is one canonical definition of how to
build/package an extensions.

### Release Notes:

- N/A

---------

Co-authored-by: Marshall <marshall@zed.dev>
Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>

crates/extensions_ui/src/components.rs

@@ -0,0 +1,3 @@
+mod extension_card;
+
+pub use extension_card::*;