Tidy up some internals of instance allocation (#5346)

* Simplify the `ModuleRuntimeInfo` trait slightly

Fold two functions into one as they're only called from one location
anyway.

* Remove ModuleRuntimeInfo::signature

This is redundant as the array mapping is already stored within the
`VMContext` so that can be consulted rather than having a separate trait
function for it. This required altering the `Global` creation slightly
to work correctly in this situation.

* Remove a now-dead constant

* Shared `VMOffsets` across instances

This commit removes the computation of `VMOffsets` to being per-module
instead of per-instance. The `VMOffsets` structure is also quite large
so this shaves off 112 bytes per instance which isn't a huge impact but
should help lower the cost of instantiating small modules.

* Remove `InstanceAllocator::adjust_tunables`

This is no longer needed or necessary with the pooling allocator.

* Fix compile warning

* Fix a vtune warning

* Fix pooling tests

* Fix another test warning

crates/jit/src/profiling/jitdump_linux.rs

@@ -83,7 +83,8 @@ impl State {
         let tid = pid; // ThreadId does appear to track underlying thread. Using PID.
 
         for (idx, func) in module.finished_functions() {
-            let (addr, len) = unsafe { ((*func).as_ptr().cast::<u8>(), (*func).len()) };
+            let addr = func.as_ptr();
+            let len = func.len();
             if let Some(img) = &dbg_image {
                 if let Err(err) = self.dump_from_debug_image(img, "wasm", addr, len, pid, tid) {
                     println!(

crates/jit/src/profiling/vtune.rs

@@ -93,7 +93,8 @@ impl State {
             .unwrap_or_else(|| format!("wasm_module_{}", global_module_id));
 
         for (idx, func) in module.finished_functions() {
-            let (addr, len) = unsafe { ((*func).as_ptr().cast::<u8>(), (*func).len()) };
+            let addr = func.as_ptr();
+            let len = func.len();
             let method_name = super::debug_name(module, idx);
             log::trace!(
                 "new function {:?}::{:?} @ {:?}\n",