Rework br_table to use BlockCall (#5731)

Rework br_table to use BlockCall, allowing us to avoid adding new nodes during ssa construction to hold block arguments. Additionally, many places where we previously matched on InstructionData to extract branch destinations can be replaced with a use of branch_destination or branch_destination_mut.

cranelift/interpreter/src/step.rs

@@ -349,8 +349,11 @@ where
     // Interpret a Cranelift instruction.
     Ok(match inst.opcode() {
         Opcode::Jump => {
-            let block = inst.branch_destination()[0];
-            continue_at(block)?
+            if let InstructionData::Jump { destination, .. } = inst {
+                continue_at(destination)?
+            } else {
+                unreachable!()
+            }
         }
         Opcode::Brif => {
             if let InstructionData::Brif {
@@ -383,7 +386,7 @@ where
                     .copied()
                     .unwrap_or(jt_data.default_block());
 
-                ControlFlow::ContinueAt(jump_target, SmallVec::new())
+                continue_at(jump_target)?
             } else {
                 unreachable!()
             }