Fill in tracking issues for const_str_from_utf8 and const_str_from_utf8_unchecked_mut features

Author: WaffleLapkin

library/core/src/str/converts.rs

@@ -82,7 +82,7 @@ use super::Utf8Error;
 /// assert_eq!("💖", sparkle_heart);
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_const_unstable(feature = "const_str_from_utf8", issue = "none")]
+#[rustc_const_unstable(feature = "const_str_from_utf8", issue = "91006")]
 pub const fn from_utf8(v: &[u8]) -> Result<&str, Utf8Error> {
     // This should use `?` again, once it's `const`
     match run_utf8_validation(v) {
@@ -125,7 +125,7 @@ pub const fn from_utf8(v: &[u8]) -> Result<&str, Utf8Error> {
 /// See the docs for [`Utf8Error`] for more details on the kinds of
 /// errors that can be returned.
 #[stable(feature = "str_mut_extras", since = "1.20.0")]
-#[rustc_const_unstable(feature = "const_str_from_utf8", issue = "none")]
+#[rustc_const_unstable(feature = "const_str_from_utf8", issue = "91006")]
 pub const fn from_utf8_mut(v: &mut [u8]) -> Result<&mut str, Utf8Error> {
     // This should use `?` again, once it's `const`
     match run_utf8_validation(v) {
@@ -196,7 +196,7 @@ pub const unsafe fn from_utf8_unchecked(v: &[u8]) -> &str {
 #[inline]
 #[must_use]
 #[stable(feature = "str_mut_extras", since = "1.20.0")]
-#[rustc_const_unstable(feature = "const_str_from_utf8_unchecked_mut", issue = "none")]
+#[rustc_const_unstable(feature = "const_str_from_utf8_unchecked_mut", issue = "91005")]
 pub const unsafe fn from_utf8_unchecked_mut(v: &mut [u8]) -> &mut str {
     // SAFETY: the caller must guarantee that the bytes `v`
     // are valid UTF-8, thus the cast to `*mut str` is safe.

library/core/src/str/error.rs

@@ -72,7 +72,7 @@ impl Utf8Error {
     /// assert_eq!(1, error.valid_up_to());
     /// ```
     #[stable(feature = "utf8_error", since = "1.5.0")]
-    #[rustc_const_unstable(feature = "const_str_from_utf8", issue = "none")]
+    #[rustc_const_unstable(feature = "const_str_from_utf8", issue = "91006")]
     #[must_use]
     #[inline]
     pub const fn valid_up_to(&self) -> usize {
@@ -95,7 +95,7 @@ impl Utf8Error {
     ///
     /// [U+FFFD]: ../../std/char/constant.REPLACEMENT_CHARACTER.html
     #[stable(feature = "utf8_error_error_len", since = "1.20.0")]
-    #[rustc_const_unstable(feature = "const_str_from_utf8", issue = "none")]
+    #[rustc_const_unstable(feature = "const_str_from_utf8", issue = "91006")]
     #[must_use]
     #[inline]
     pub const fn error_len(&self) -> Option<usize> {