keysym-utf: replace the Unicode characters for leftanglebracket and rightanglebracket

keysym-utf: replace the Unicode characters for leftanglebracket and rightanglebracket

Looking at leftanglebracket

- The standard[1] does not specify any Unicode value for it.

- The keysym list keysymdef.h in x11proto[2] says U+27E9 MATHEMATICAL
  RIGHT ANGLE BRACKET in a comment.

- The keysym->unicode list in xkbcommon which comes from [3] has U+2329
  LEFT-POINTING ANGLE BRACKET.

- The keysym->unicode list in Xlib[4] has U+2039 SINGLE LEFT-POINTING
  ANGLE QUOTATION MARK.

[1] https://www.x.org/releases/X11R7.7/doc/xproto/x11protocol.html#Legacy_KEYSYMs
[2] https://cgit.freedesktop.org/xorg/proto/x11proto/tree/keysymdef.h
[3] https://www.cl.cam.ac.uk/%7Emgk25/ucs/keysym2ucs.c
[4] https://cgit.freedesktop.org/xorg/lib/libX11/tree/src/xlibi18n/imKStoUCS.c

The symbols we are using, {LEFT,RIGHT}-POINTING ANGLE BRACKET, are
deprecated according to Unicode[5]:

    These characters are deprecated and are strongly discouraged for
    mathematical use because of their canonical equivalence to CJK
    punctuation.

[5] https://www.unicode.org/charts/PDF/U2300.pdf

Hence, switch to the MATHEMATICAL codepoints which seem to be the best
fit.

Fixes: https://github.com/xkbcommon/libxkbcommon/issues/47
Reported-by: @bytensky
Signed-off-by: Ran Benita <ran234@gmail.com>