Copy extension_api Rust files to OUT_DIR when building extension to work around rust-analyzer limitation (#16064)

Copies rust files from extension_api/wit to the OUT_DIR to allow
including them from within the crate, which is supported by
rust-analyzer. This allows rust-analyzer to deal with the included
files. It doesn't currently support files outside the crate.

Release Notes:

- N/A

crates/extension/src/wasm_host/wit/since_v0_0_6.rs

@@ -23,7 +23,7 @@ wasmtime::component::bindgen!({
 });
 
 mod settings {
-    include!("../../../../extension_api/wit/since_v0.0.6/settings.rs");
+    include!(concat!(env!("OUT_DIR"), "/since_v0.0.6/settings.rs"));
 }
 
 pub type ExtensionWorktree = Arc<dyn LspAdapterDelegate>;

crates/extension/src/wasm_host/wit/since_v0_0_7.rs

@@ -37,7 +37,7 @@ wasmtime::component::bindgen!({
 pub use self::zed::extension::*;
 
 mod settings {
-    include!("../../../../extension_api/wit/since_v0.0.7/settings.rs");
+    include!(concat!(env!("OUT_DIR"), "/since_v0.0.7/settings.rs"));
 }
 
 pub type ExtensionWorktree = Arc<dyn LspAdapterDelegate>;