[libc] finish documenting c23 additions (#84383)

- [libc] finish documenting c23 additions
- sort according to appearance in Annex B and section 7

Author: nickdesaulniers

libc/docs/c23.rst

@@ -15,36 +15,15 @@ Implementation Status
 
 (It's helpful to review 'Annex B (Informative) Library Summary' for these.)
 
-New headers:
-
-* stdbit.h
-* stdckdint.h (|check|, macros are only defined with `__GNUC__` builtins)
 
 Additions:
 
-* uchar.h
-
-  * mbrtoc8
-  * c8rtomb
-  * char*_t
-
-* string.h
-
-  * memset_explicit
-  * memccpy
-  * strdup
-  * strndup
-
-* time.h
-
-  * gmtime_r
-  * localtime_r
-  * timegm
-  * timespec_getres
-  * strftime conversion specifiers
+* fenv.h
 
-    * 0b
-    * 0B
+  * fesetexcept
+  * fetestexceptflag
+  * fegetmode
+  * fesetmode
 * math.h
 
   * acospi*
@@ -96,20 +75,87 @@ Additions:
   * dfmal
   * fsqrt*
   * dsqrtl
-* fenv.h
-
-  * fesetexcept
-  * fetestexceptflag
-  * fegetmode
-  * fesetmode
+* stdbit.h (New header)
+* stdckdint.h (New header) |check|
 * stddef.h
 
   * unreachable
 * stdlib.h
 
+  * strfromd
+  * strfromf
+  * strfroml
   * free_sized
   * free_aligned_sized
   * memalignment
+* string.h
+
+  * memset_explicit |check|
+  * memccpy
+  * strdup
+  * strndup
 * tgmath.h
 
-  * <TODO>
+  * acospi
+  * asinpi
+  * atan2pi
+  * atanpi
+  * compoundn
+  * cospi
+  * erf
+  * exp10m1
+  * exp10
+  * exp2m1
+  * fmaximum
+  * fmaximum_mag
+  * fmaximum_num
+  * fmaximum_mag_num
+  * fminimum
+  * fminimum_mag
+  * fminimum_num
+  * fminimum_mag_num
+  * fromfpx
+  * fromfp
+  * llogb
+  * log10p1
+  * log2p1
+  * logp1
+  * nextdown
+  * nextup
+  * pown
+  * powr
+  * rootn
+  * roundeven
+  * rsqrt
+  * scalbn
+  * sinpi
+  * tanpi
+  * ufromfpx
+  * ufromfp
+  * fadd
+  * dadd
+  * fsub
+  * dsub
+  * fmul
+  * dmul
+  * fdiv
+  * ddiv
+  * ffma
+  * dfma
+  * fsqrt
+  * dsqrt
+* time.h
+
+  * gmtime_r
+  * localtime_r
+  * timegm
+  * timespec_getres
+  * strftime conversion specifiers
+
+    * 0b
+    * 0B
+* uchar.h
+
+  * mbrtoc8
+  * c8rtomb
+  * char*_t