Eliminate most 'deprecated declarations' warnings

[jkeenan]

If I build Tk-804.036 against a Perl executable built on Linux and compiled with gcc-13 (currently the most recent version of gcc against which Tk's make will complete), I get the following count of build-time warnings:

$ report-build-warnings 804.036-0-gcc-13.make.output.txt 
File:  804.036-0-gcc-13.make.output.txt

  Wdeprecated-declarations                   9
  Wdiscarded-qualifiers                      1
  Wformat-overflow=                          5
  Wimplicit-int                              3
  Wincompatible-pointer-types                7
  Wint-to-pointer-cast                      42
  Wpointer-to-int-cast                      25
  Wstringop-overflow=                        1

The patches in this pull request, when applied will reduce the number of Wdeprecated-declarations warnings from 9 to 1.

$ report-build-warnings 07ef24a882.gcc13.make.output.txt 
File:  07ef24a882.gcc13.make.output.txt

  Wdeprecated-declarations                   1
  Wdiscarded-qualifiers                      1
  Wformat-overflow=                          5
  Wimplicit-function-declaration             1
  Wimplicit-int                              3
  Wincompatible-pointer-types                7
  Wint-to-pointer-cast                      42
  Wpointer-to-int-cast                      25
  Wstringop-overflow=                        1

For changes in tkUnixKey.c, consult DDG search for "XKeycodeToKeysym is deprecated".

For changes in Event/Event.xs, see perldoc perl5380delta.

The one remaining Wdeprecated-declarations build-time warning appears during make like this:

In file included from Xlib_f.c:17:
Xlib.t:334:1: warning: ‘XKeycodeToKeysym’ is deprecated [-Wdeprecated-declarations]
  334 | VFUNC(KeySym,XKeycodeToKeysym,V_XKeycodeToKeysym,_ANSI_ARGS_((Display *, unsigned int, int)))
      | ^~~~~

And here's the relevant source code in pTk/Xlib.t:

333 #ifndef XKeycodeToKeysym
334 VFUNC(KeySym,XKeycodeToKeysym,V_XKeycodeToKeysym,_ANSI_ARGS_((Display *, unsigned int, int)))
335 #endif /* #ifndef XKeycodeToKeysym */

A simple search-and-replace, XKeycodeToKeysym -> XkbKeycodeToKeysym, did not compile, so I left this instance alone.