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

tests/all/pooling_allocator.rs

@@ -646,10 +646,11 @@ fn instance_too_large() -> Result<()> {
 
     let engine = Engine::new(&config)?;
     let expected = "\
-instance allocation for this module requires 336 bytes which exceeds the \
+instance allocation for this module requires 224 bytes which exceeds the \
 configured maximum of 16 bytes; breakdown of allocation requirement:
 
- * 76.19% - 256 bytes - instance state management
+ * 64.29% - 144 bytes - instance state management
+ * 7.14% - 16 bytes - jit store state
 ";
     match Module::new(&engine, "(module)") {
         Ok(_) => panic!("should have failed to compile"),
@@ -663,11 +664,11 @@ configured maximum of 16 bytes; breakdown of allocation requirement:
     lots_of_globals.push_str(")");
 
     let expected = "\
-instance allocation for this module requires 1936 bytes which exceeds the \
+instance allocation for this module requires 1824 bytes which exceeds the \
 configured maximum of 16 bytes; breakdown of allocation requirement:
 
- * 13.22% - 256 bytes - instance state management
- * 82.64% - 1600 bytes - defined globals
+ * 7.89% - 144 bytes - instance state management
+ * 87.72% - 1600 bytes - defined globals
 ";
     match Module::new(&engine, &lots_of_globals) {
         Ok(_) => panic!("should have failed to compile"),