implement Component Model async ABI

This commit replaces the stub functions and types in
`wasmtime::runtime::component::concurrent` and its submodules with the working
implementation developed in the `wasip3-prototyping` repo.  For ease of review,
it does not include any new tests; I'll add those in a follow-up commit.

Note that this builds on #11123; only the most recent commit is new.

Signed-off-by: Joel Dice <[email protected]>

Author: dicej

crates/wasmtime/src/runtime/component/concurrent.rs

@@ -0,0 +1,16 @@
+/// Error context reference count local to a given (sub)component
+///
+/// This reference count is localized to a single (sub)component,
+/// rather than the global cross-component count (i.e. that determines
+/// when a error context can be completely removed)
+#[repr(transparent)]
+pub struct LocalErrorContextRefCount(pub(crate) usize);
+
+/// Error context reference count across a [`ComponentInstance`]
+///
+/// Contrasted to `LocalErrorContextRefCount`, this count is maintained
+/// across all sub-components in a given component.
+///
+/// When this count is zero it is *definitely* safe to remove an error context.
+#[repr(transparent)]
+pub struct GlobalErrorContextRefCount(pub(crate) usize);