curlx: curlx_strcopy() instead of strcpy()

This function REQUIRES the size of the target buffer as well as the
length of the source string. Meant to make it harder to do a bad
strcpy().

Removes 23 calls to strcpy().

Closes #20067

lib/Makefile.inc

@@ -31,6 +31,7 @@ LIB_CURLX_CFILES = \
   curlx/inet_pton.c \
   curlx/multibyte.c \
   curlx/nonblock.c \
+  curlx/strcopy.c  \
   curlx/strerr.c   \
   curlx/strparse.c \
   curlx/timediff.c \
@@ -51,6 +52,7 @@ LIB_CURLX_HFILES = \
   curlx/multibyte.h \
   curlx/nonblock.h \
   curlx/snprintf.h \
+  curlx/strcopy.h  \
   curlx/strerr.h   \
   curlx/strparse.h \
   curlx/timediff.h \