Convert last vestiges of to/from 'uvchr' to 'uv'

We are trying to encourage new code to use the latter form, so use it in
the remaining pod examples that still used 'uvchr'

This also corrects the common entry  for uv_to_utf8_msgs() and
uvchr_to_utf8_flags_msgs() to be cognizant that there are two identical
functions.

Author: khwilliamson

pod/perlguts.pod

@@ -3568,15 +3568,18 @@ whether the byte is encoded as a single byte even in UTF-8):
                     char */
     STRLEN len; /* Returned length of character in bytes */
 
-    if (!UTF8_IS_INVARIANT(*utf))
+    if (!UTF8_IS_INVARIANT(*utf)) {
         /* Must treat this as UTF-8 */
-        uv = utf8_to_uvchr_buf(utf, utf_end, &len);
+        if (! utf8_to_uv(utf, utf_end, &uv, &len)) {
+            /* handle error */
+        }
+    }
     else
         /* OK to treat this character as a byte */
         uv = *utf;
 
-You can also see in that example that we use C<utf8_to_uvchr_buf> to get the
-value of the character; the inverse function C<uvchr_to_utf8> is available
+You can also see in that example that we use C<utf8_to_uv> to get the
+value of the character; the inverse function C<uv_to_utf8> is available
 for putting a UV into UTF-8:
 
     if (!UVCHR_IS_INVARIANT(uv))
@@ -3794,7 +3797,7 @@ the PV to somewhere, pass on the flag too.
 
 =item *
 
-If a string is UTF-8, B<always> use C<utf8_to_uvchr_buf> to get at the value,
+If a string is UTF-8, B<always> use C<utf8_to_uv> to get at the value,
 unless C<UTF8_IS_INVARIANT(*s)> in which case you can use C<*s>.
 
 =item *

utf8.c

@@ -123,19 +123,19 @@ const char super_cp_format[]     = "Code point 0x%" UVXf " is not Unicode,"
 =for apidoc_item uvchr_to_utf8_flags_msgs
 
 These functions are identical.  THEY SHOULD BE USED IN ONLY VERY SPECIALIZED
-CIRCUMSTANCES.
+CIRCUMSTANCES.  The C<uv_to_utf8_msgs> spelling is preferred in new code.
 
-Most code should use C<L</uv_to_utf8_flags>()> rather than call this directly.
+Most code should use C<L</uv_to_utf8_flags>()> rather than call these directly.
 
-This function is for code that wants any warning and/or error messages to be
+These functions are for code that wants any warning and/or error messages to be
 returned to the caller rather than be displayed.  Any message that would have
 been displayed if all lexical warnings are enabled will instead be returned.
 
-It is just like C<L</uvchr_to_utf8_flags>> but it takes an extra parameter
-placed after all the others, C<msgs>.  If this parameter is 0, this function
-behaves identically to C<L</uvchr_to_utf8_flags>>.  Otherwise, C<msgs> should
-be a pointer to an C<HV *> variable, in which this function creates a new HV to
-contain any appropriate message.  The hash has three key-value pairs, as
+They are just like C<L</uv_to_utf8_flags>> but take an extra parameter
+placed after all the others, C<msgs>.  If this parameter is 0, the functions
+behave identically to C<L</uv_to_utf8_flags>>.  Otherwise, C<msgs> should
+be a pointer to an C<HV *> variable, in which these functions create a new HV
+to contain any appropriate message.  The hash has three key-value pairs, as
 follows:
 
 =over 4
@@ -169,7 +169,7 @@ The possibilities are:
 =back
 
 It's important to note that specifying this parameter as non-null will cause
-any warning this function would otherwise generate to be suppressed, and
+any warning the functions would otherwise generate to be suppressed, and
 instead be placed in C<*msgs>.  The caller can check the lexical warnings state
 (or not) when choosing what to do with the returned message.