Call 'format!' through an unambiguous path

Repro:

    use quote::format_ident;

    macro_rules! format {
        () => {};
    }

    fn main() {
        let _ = format_ident!("foo");
    }

Previously:

    error: no rules expected the token `"foo"`
     --> src/main.rs:8:13
      |
    3 | macro_rules! format {
      | ------------------- when calling this macro
    ...
    8 |     let _ = format_ident!("foo");
      |             ^^^^^^^^^^^^^^^^^^^^ no rules expected this token in macro call
      |
      = note: this error originates in the macro `format_ident` (in Nightly builds, run with -Z macro-backtrace for more info)

src/format.rs

@@ -129,7 +129,10 @@ macro_rules! format_ident {
 macro_rules! format_ident_impl {
     // Final state
     ([$span:expr, $($fmt:tt)*]) => {
-        $crate::__private::mk_ident(&format!($($fmt)*), $span)
+        $crate::__private::mk_ident(
+            &$crate::__private::format!($($fmt)*),
+            $span,
+        )
     };
 
     // Span argument

src/runtime.rs

@@ -4,6 +4,7 @@ use std::iter;
 use std::ops::BitOr;
 
 pub use proc_macro2::*;
+pub use std::format;
 
 pub struct HasIterator; // True
 pub struct ThereIsNoIteratorInRepetition; // False