Implement canon lower of a canon lift function in the same component (#4347)

* Implement `canon lower` of a `canon lift` function in the same component

This commit implements the "degenerate" logic for implementing a
function within a component that is lifted and then immediately lowered
again. In this situation the lowered function will immediately generate
a trap and doesn't need to implement anything else.

The implementation in this commit is somewhat heavyweight but I think is
probably justified moreso in future additions to the component model
rather than what exactly is here right now. It's not expected that this
"always trap" functionality will really be used all that often since it
would generally mean a buggy component, but the functionality plumbed
through here is hopefully going to be useful for implementing
component-to-component adapter trampolines.

Specifically this commit implements a strategy where the `canon.lower`'d
function is generated by Cranelift and simply has a single trap
instruction when called, doing nothing else. The main complexity comes
from juggling around all the data associated with these functions,
primarily plumbing through the traps into the `ModuleRegistry` to
ensure that the global `is_wasm_trap_pc` function returns `true` and at
runtime when we lookup information about the trap it's all readily
available (e.g. translating the trapping pc to a `TrapCode`).

* Fix non-component build

* Fix some offset calculations

* Only create one "always trap" per signature

Use an internal map to deduplicate during compilation.

crates/environ/src/component/info.rs

@@ -143,6 +143,10 @@ pub struct Component {
     /// The number of modules that are required to be saved within an instance
     /// at runtime, or effectively the number of exported modules.
     pub num_runtime_modules: u32,
+
+    /// The number of functions which "always trap" used to implement
+    /// `canon.lower` of `canon.lift`'d functions within the same component.
+    pub num_always_trap: u32,
 }
 
 /// GlobalInitializer instructions to get processed when instantiating a component
@@ -173,6 +177,12 @@ pub enum GlobalInitializer {
     /// pointer the trampoline calls, and the canonical ABI options.
     LowerImport(LowerImport),
 
+    /// A core wasm function was "generated" via `canon lower` of a function
+    /// that was `canon lift`'d in the same component, meaning that the function
+    /// always traps. This is recorded within the `VMComponentContext` as a new
+    /// `VMCallerCheckedAnyfunc` that's available for use.
+    AlwaysTrap(AlwaysTrap),
+
     /// A core wasm linear memory is going to be saved into the
     /// `VMComponentContext`.
     ///
@@ -272,6 +282,17 @@ pub struct LowerImport {
     pub options: CanonicalOptions,
 }
 
+/// Description of what to initialize when a `GlobalInitializer::AlwaysTrap` is
+/// encountered.
+#[derive(Debug, Serialize, Deserialize)]
+pub struct AlwaysTrap {
+    /// The index of the function that is being initialized in the
+    /// `VMComponentContext`.
+    pub index: RuntimeAlwaysTrapIndex,
+    /// The core wasm signature of the function that's inserted.
+    pub canonical_abi: SignatureIndex,
+}
+
 /// Definition of a core wasm item and where it can come from within a
 /// component.
 ///
@@ -288,6 +309,10 @@ pub enum CoreDef {
     /// that this `LoweredIndex` corresponds to the nth
     /// `GlobalInitializer::LowerImport` instruction.
     Lowered(LoweredIndex),
+    /// This is used to represent a degenerate case of where a `canon lift`'d
+    /// function is immediately `canon lower`'d in the same instance. Such a
+    /// function always traps at runtime.
+    AlwaysTrap(RuntimeAlwaysTrapIndex),
 }
 
 impl<T> From<CoreExport<T>> for CoreDef