Cranelift: Add heap_load and heap_store instructions (#5300)

* Cranelift: Define `heap_load` and `heap_store` instructions

* Cranelift: Implement interpreter support for `heap_load` and `heap_store`

* Cranelift: Add a suite runtests for `heap_{load,store}`

There are so many knobs we can twist for heaps and I wanted to exhaustively test
all of them, so I wrote a script to generate the tests. I've checked in the
script in case we want to make any changes in the future, but I don't think it
is worth adding this to CI to check that scripts are up to date or anything like
that.

* Review feedback

cranelift/codegen/src/ir/mod.rs

@@ -37,8 +37,8 @@ pub use crate::ir::constant::{ConstantData, ConstantPool};
 pub use crate::ir::dfg::{DataFlowGraph, ValueDef};
 pub use crate::ir::dynamic_type::{dynamic_to_fixed, DynamicTypeData, DynamicTypes};
 pub use crate::ir::entities::{
-    Block, Constant, DynamicStackSlot, DynamicType, FuncRef, GlobalValue, Heap, Immediate, Inst,
-    JumpTable, SigRef, StackSlot, Table, UserExternalNameRef, Value,
+    Block, Constant, DynamicStackSlot, DynamicType, FuncRef, GlobalValue, Heap, HeapImm, Immediate,
+    Inst, JumpTable, SigRef, StackSlot, Table, UserExternalNameRef, Value,
 };
 pub use crate::ir::extfunc::{
     AbiParam, ArgumentExtension, ArgumentPurpose, ExtFuncData, Signature,