[Utils] Add highlighting definition for byref IR attribute

[atrosinenko]

Summary

This patch assumes byref can be handled identically to byval.

The Kate and Vim highlighting definitions were basically checked, the VSCode one is expected to work due to its simplicity.

[guiand]

LGTM, but I don't really maintain this code.

llvm/utils/kate/llvm.xml

<list name="visibility-styles">
       <item> default </item>
       <item> hidden </item>
       <item> protected </item>
     </list>
     <list name="parameter-attributes">
       <item> zeroext </item>
       <item> signext </item>
       <item> inreg </item>
+      <item> byref </item>
       <item> byval </item>
       <item> sret </item>
       <item> noalias </item>
       <item> nocapture </item>
       <item> nest </item>
     </list>
     <list name="function-attributes">
       <item> alignstack </item>

llvm/utils/vim/syntax/llvm.vim

syn keyword llvmKeyword
       \ arm_aapcscc
       \ arm_aapcs_vfpcc
       \ arm_apcscc
       \ asm
       \ atomic
       \ available_externally
       \ blockaddress
       \ builtin
+      \ byref
       \ byval
       \ c
       \ catch
       \ caller
       \ cc
       \ ccc
       \ cleanup
       \ coldcc

llvm/utils/vscode/llvm/syntaxes/ll.tmLanguage.yaml

- match: "\\bacq_rel\\b|\
             \\barm_aapcscc\\b|\
             \\barm_aapcs_vfpcc\\b|\
             \\barm_apcscc\\b|\
             \\basm\\b|\
             \\batomic\\b|\
             \\bavailable_externally\\b|\
             \\bblockaddress\\b|\
             \\bbuiltin\\b|\
+            \\bbyref\\b|\
             \\bbyval\\b|\
             \\bc\\b|\
             \\bcatch\\b|\
             \\bcaller\\b|\
             \\bcc\\b|\
             \\bccc\\b|\
             \\bcleanup\\b|\
             \\bcoldcc\\b|\