Rollup merge of #110766 - m-ou-se:fmt-rt, r=jyn514

More core::fmt::rt cleanup.

- Removes the `V1` suffix from the `Argument` and `Flag` types.

- Moves more of the format_args lang items into the `core::fmt::rt` module. (The only remaining lang item in `core::fmt` is `Arguments` itself, which is a public type.)

Part of rust-lang/rust#99012

Follow-up to rust-lang/rust#110616

crates/hir-def/src/macro_expansion_tests/builtin_fn_macro.rs

@@ -201,7 +201,7 @@ macro_rules! format_args {
 }
 
 fn main() {
-    $crate::fmt::Arguments::new_v1(&[], &[$crate::fmt::ArgumentV1::new(&(arg1(a, b, c)), $crate::fmt::Display::fmt), $crate::fmt::ArgumentV1::new(&(arg2), $crate::fmt::Display::fmt), ]);
+    $crate::fmt::Arguments::new_v1(&[], &[$crate::fmt::Argument::new(&(arg1(a, b, c)), $crate::fmt::Display::fmt), $crate::fmt::Argument::new(&(arg2), $crate::fmt::Display::fmt), ]);
 }
 "#]],
     );
@@ -229,7 +229,7 @@ macro_rules! format_args {
 }
 
 fn main() {
-    $crate::fmt::Arguments::new_v1(&[], &[$crate::fmt::ArgumentV1::new(&(a::<A, B>()), $crate::fmt::Display::fmt), $crate::fmt::ArgumentV1::new(&(b), $crate::fmt::Display::fmt), ]);
+    $crate::fmt::Arguments::new_v1(&[], &[$crate::fmt::Argument::new(&(a::<A, B>()), $crate::fmt::Display::fmt), $crate::fmt::Argument::new(&(b), $crate::fmt::Display::fmt), ]);
 }
 "#]],
     );
@@ -260,7 +260,7 @@ macro_rules! format_args {
 fn main() {
     let _ =
         /* parse error: expected field name or number */
-$crate::fmt::Arguments::new_v1(&[], &[$crate::fmt::ArgumentV1::new(&(a.), $crate::fmt::Display::fmt), ]);
+$crate::fmt::Arguments::new_v1(&[], &[$crate::fmt::Argument::new(&(a.), $crate::fmt::Display::fmt), ]);
 }
 "#]],
     );

crates/hir-expand/src/builtin_fn_macro.rs

@@ -241,8 +241,8 @@ fn format_args_expand(
     // We expand `format_args!("", a1, a2)` to
     // ```
     // $crate::fmt::Arguments::new_v1(&[], &[
-    //   $crate::fmt::ArgumentV1::new(&arg1,$crate::fmt::Display::fmt),
-    //   $crate::fmt::ArgumentV1::new(&arg2,$crate::fmt::Display::fmt),
+    //   $crate::fmt::Argument::new(&arg1,$crate::fmt::Display::fmt),
+    //   $crate::fmt::Argument::new(&arg2,$crate::fmt::Display::fmt),
     // ])
     // ```,
     // which is still not really correct, but close enough for now
@@ -267,7 +267,7 @@ fn format_args_expand(
     }
     let _format_string = args.remove(0);
     let arg_tts = args.into_iter().flat_map(|arg| {
-        quote! { #DOLLAR_CRATE::fmt::ArgumentV1::new(&(#arg), #DOLLAR_CRATE::fmt::Display::fmt), }
+        quote! { #DOLLAR_CRATE::fmt::Argument::new(&(#arg), #DOLLAR_CRATE::fmt::Display::fmt), }
     }.token_trees);
     let expanded = quote! {
         #DOLLAR_CRATE::fmt::Arguments::new_v1(&[], &[##arg_tts])