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/meta/src/shared/formats.rs

@@ -16,6 +16,8 @@ pub(crate) struct Formats {
     pub(crate) float_compare: Rc<InstructionFormat>,
     pub(crate) func_addr: Rc<InstructionFormat>,
     pub(crate) heap_addr: Rc<InstructionFormat>,
+    pub(crate) heap_load: Rc<InstructionFormat>,
+    pub(crate) heap_store: Rc<InstructionFormat>,
     pub(crate) int_compare: Rc<InstructionFormat>,
     pub(crate) int_compare_imm: Rc<InstructionFormat>,
     pub(crate) int_add_trap: Rc<InstructionFormat>,
@@ -206,6 +208,17 @@ impl Formats {
                 .imm_with_name("size", &imm.uimm8)
                 .build(),
 
+            heap_load: Builder::new("HeapLoad").imm(&imm.heap_imm).value().build(),
+
+            heap_store: Builder::new("HeapStore")
+                // We have more fields for this instruction than
+                // `InstructionData` can hold without growing in size, so we
+                // push the immediates out into a side table.
+                .imm(&imm.heap_imm)
+                .value()
+                .value()
+                .build(),
+
             // Accessing a WebAssembly table.
             table_addr: Builder::new("TableAddr")
                 .imm(&entities.table)