Don't initialize interactive reader redundantly

Commands like

	fish -C 'read'

create two top-level readers one after the other.  The second one is
the fish REPL.

Both run some initialization of globals and parser variables.  This is
weird; it should not be necessary.

Let's call reader_interactive_init() only once.

src/parser.rs

@@ -404,6 +404,8 @@ pub enum CancelBehavior {
 }
 
 pub struct Parser {
+    pub interactive_initialized: RelaxedAtomicBool,
+
     /// A shared line counter. This is handed out to each execution context
     /// so they can communicate the line number back to this Parser.
     line_counter: ScopedRefCell<LineCounter<ast::JobPipeline>>,
@@ -449,6 +451,7 @@ impl Parser {
     /// Create a parser.
     pub fn new(variables: EnvStack, cancel_behavior: CancelBehavior) -> Parser {
         let result = Self {
+            interactive_initialized: RelaxedAtomicBool::new(false),
             line_counter: ScopedRefCell::new(LineCounter::empty()),
             job_list: RefCell::default(),
             wait_handles: RefCell::new(WaitHandleStore::new()),

src/reader.rs

@@ -315,12 +315,11 @@ pub fn reader_push<'a>(parser: &'a Parser, history_name: &wstr, conf: ReaderConf
     assert_is_main_thread();
     let hist = History::with_name(history_name);
     hist.resolve_pending();
-    let is_top_level = reader_data_stack().is_empty();
-    let data = ReaderData::new(hist, conf, is_top_level);
+    let data = ReaderData::new(hist, conf, reader_data_stack().is_empty());
     reader_data_stack().push(data);
     let data = current_data().unwrap();
     data.command_line_changed(EditableLineTag::Commandline, AutosuggestionUpdate::Remove);
-    if is_top_level {
+    if !parser.interactive_initialized.swap(true) {
         reader_interactive_init(parser);
     }
     Reader { data, parser }
@@ -335,7 +334,7 @@ pub fn reader_pop() {
             .screen
             .reset_abandoning_line(usize::try_from(termsize_last().width).unwrap());
     } else {
-        reader_interactive_destroy();
+        Outputter::stdoutput().borrow_mut().reset_text_face();
         *commandline_state_snapshot() = CommandlineState::new();
     }
 }
@@ -4548,11 +4547,6 @@ fn reader_interactive_init(parser: &Parser) {
     initialize_tty_metadata();
 }
 
-/// Destroy data for interactive use.
-fn reader_interactive_destroy() {
-    Outputter::stdoutput().borrow_mut().reset_text_face();
-}
-
 /// Return whether fish is currently unwinding the stack in preparation to exit.
 pub fn fish_is_unwinding_for_exit() -> bool {
     let exit_state = EXIT_STATE.load(Ordering::Relaxed);