rust: str: expose str::Formatter::new publicly.

rnull is going to make use of `str::Formatter`, so expose it with public
visibility.

Signed-off-by: Andreas Hindborg <[email protected]>

Author: Andreas Hindborg

rust/kernel/str.rs

@@ -703,7 +703,7 @@ mod tests {
 ///
 /// The memory region between `pos` (inclusive) and `end` (exclusive) is valid for writes if `pos`
 /// is less than `end`.
-pub(crate) struct RawFormatter {
+pub struct RawFormatter {
     // Use `usize` to use `saturating_*` functions.
     beg: usize,
     pos: usize,
@@ -795,7 +795,7 @@ impl fmt::Write for RawFormatter {
 /// Allows formatting of [`fmt::Arguments`] into a raw buffer.
 ///
 /// Fails if callers attempt to write more than will fit in the buffer.
-pub(crate) struct Formatter<'a>(RawFormatter, PhantomData<&'a mut ()>);
+pub struct Formatter<'a>(RawFormatter, PhantomData<&'a mut ()>);
 
 impl Formatter<'_> {
     /// Creates a new instance of [`Formatter`] with the given buffer.
@@ -810,8 +810,7 @@ impl Formatter<'_> {
     }
 
     /// Create a new [`Self`] instance.
-    #[expect(dead_code)]
-    pub(crate) fn new<'a>(buffer: &'a mut [u8]) -> Formatter<'a> {
+    pub fn new<'a>(buffer: &'a mut [u8]) -> Formatter<'a> {
         // SAFETY: `buffer` is valid for writes for the entire length for
         // the lifetime of `Self`.
         unsafe { Formatter::from_buffer(buffer.as_mut_ptr(), buffer.len()) }