Add a type parameter to VMOffsets for pointer size (#3020)

* Add a type parameter to `VMOffsets` for pointer size

This commit adds a type parameter to `VMOffsets` representing the
pointer size to improve computations in `wasmtime-runtime` which always
use a constant value of the host's pointer size. The type parameter is
`u8` for `wasmtime-cranelift`'s use case where cross-compilation may be
involved.

* fix lightbeam

crates/runtime/src/instance.rs

@@ -27,7 +27,7 @@ use wasmtime_environ::wasm::{
     DataIndex, DefinedGlobalIndex, DefinedMemoryIndex, DefinedTableIndex, ElemIndex, EntityIndex,
     FuncIndex, GlobalIndex, MemoryIndex, TableElementType, TableIndex, WasmType,
 };
-use wasmtime_environ::{ir, Module, VMOffsets};
+use wasmtime_environ::{ir, HostPtr, Module, VMOffsets};
 
 mod allocator;
 
@@ -119,7 +119,7 @@ pub(crate) struct Instance {
     module: Arc<Module>,
 
     /// Offsets in the `vmctx` region, precomputed from the `module` above.
-    offsets: VMOffsets,
+    offsets: VMOffsets<HostPtr>,
 
     /// WebAssembly linear memory data.
     ///