LibJS: Shrink two u64 fields in ExecutionContext to u32

To shrink ExecutionContext, these two fields are made 32-bit:

- skip_when_determining_incumbent_counter
- program_counter

Libraries/LibJS/Bytecode/Interpreter.cpp

@@ -305,7 +305,7 @@ ThrowCompletionOr<Value> Interpreter::run(SourceTextModule& module)
     return js_undefined();
 }
 
-NEVER_INLINE Interpreter::HandleExceptionResponse Interpreter::handle_exception(size_t& program_counter, Value exception)
+NEVER_INLINE Interpreter::HandleExceptionResponse Interpreter::handle_exception(u32& program_counter, Value exception)
 {
     reg(Register::exception()) = exception;
     m_scheduled_jump = {};
@@ -349,7 +349,7 @@ FLATTEN_ON_CLANG void Interpreter::run_bytecode(size_t entry_point)
     auto& executable = current_executable();
     auto const* bytecode = executable.bytecode.data();
 
-    size_t& program_counter = running_execution_context.program_counter;
+    u32& program_counter = running_execution_context.program_counter;
     program_counter = entry_point;
 
     // Declare a lookup table for computed goto with each of the `handle_*` labels

Libraries/LibJS/Bytecode/Interpreter.h

@@ -95,7 +95,7 @@ private:
         ExitFromExecutable,
         ContinueInThisExecutable,
     };
-    [[nodiscard]] HandleExceptionResponse handle_exception(size_t& program_counter, Value exception);
+    [[nodiscard]] HandleExceptionResponse handle_exception(u32& program_counter, Value exception);
 
     VM& m_vm;
     Optional<size_t> m_scheduled_jump;

Libraries/LibJS/Runtime/ExecutionContext.h

@@ -58,7 +58,11 @@ public:
     // Non-standard: This points at something that owns this ExecutionContext, in case it needs to be protected from GC.
     GC::Ptr<Cell> context_owner;
 
-    size_t program_counter { 0 };
+    u32 program_counter { 0 };
+
+    // https://html.spec.whatwg.org/multipage/webappapis.html#skip-when-determining-incumbent-counter
+    // FIXME: Move this out of LibJS (e.g. by using the CustomData concept), as it's used exclusively by LibWeb.
+    u32 skip_when_determining_incumbent_counter { 0 };
 
     mutable RefPtr<CachedSourceRange> cached_source_range;
 
@@ -66,10 +70,6 @@ public:
 
     GC::Ptr<Bytecode::Executable> executable;
 
-    // https://html.spec.whatwg.org/multipage/webappapis.html#skip-when-determining-incumbent-counter
-    // FIXME: Move this out of LibJS (e.g. by using the CustomData concept), as it's used exclusively by LibWeb.
-    size_t skip_when_determining_incumbent_counter { 0 };
-
     Span<Value> registers_and_constants_and_locals_and_arguments_span()
     {
         return { registers_and_constants_and_locals_and_arguments(), registers_and_constants_and_locals_and_arguments_count };

Libraries/LibWeb/HTML/Scripting/Environments.cpp

@@ -207,9 +207,10 @@ void prepare_to_run_callback(JS::Realm& realm)
     auto* context = top_most_script_having_execution_context(vm);
 
     // 3. If context is not null, increment context's skip-when-determining-incumbent counter.
-    if (context)
+    if (context) {
         context->skip_when_determining_incumbent_counter++;
     }
+}
 
 // https://html.spec.whatwg.org/multipage/urls-and-fetching.html#parse-a-url
 Optional<URL::URL> EnvironmentSettingsObject::parse_url(StringView url)
@@ -265,8 +266,9 @@ void clean_up_after_running_callback(JS::Realm const& realm)
     auto* context = top_most_script_having_execution_context(vm);
 
     // 2. If context is not null, decrement context's skip-when-determining-incumbent counter.
-    if (context)
+    if (context) {
         context->skip_when_determining_incumbent_counter--;
+    }
 
     // 3. Assert: the topmost entry of the backup incumbent realm stack is realm.
     auto& event_loop = HTML::main_thread_event_loop();