Insert null checks for pointer dereferences when debug assertions are enabled

Similar to how the alignment is already checked, this adds a check
for null pointer dereferences in debug mode. It is implemented similarly
to the alignment check as a MirPass.

This is related to a 2025H1 project goal for better UB checks in debug
mode: https://github.com/rust-lang/rust-project-goals/pull/177.

crates/intern/src/symbol/symbols.rs

@@ -363,6 +363,7 @@ define_symbols! {
     panic_location,
     panic_misaligned_pointer_dereference,
     panic_nounwind,
+    panic_null_pointer_dereference,
     panic,
     Param,
     parse,