bug#14645: Keep highlighting face foreground

[Juri Linkov]

>> Another place where `add-face-text-property' could help is for the
>> recently added face `info-index-match'.  Currently it looks very ugly
>> when the `info-index-match' face is added in the middle of a link
>> that breaks its continuity.  A test case is: `C-h r I match RET'.
>>
>> This is because `Info-index' adds the `info-index-match' face to the
>> strings of the found index entries.  Later `Info-virtual-index-find-node'
>> inserts strings to the Info buffer.  And finally `Info-fontify-node'
>> puts the `font-lock-face' property with `info-xref' on links.
>> The `face info-index-match' takes precedence over `font-lock-face info-xref'.
>
> This hadn't been fixed, so I applied your patch to Emacs 28.

This patch breaks Info fontification, please revert it.
Here is what I said in the message sent later with another patch at
https://debbugs.gnu.org/14645#14

  Using the text property `face' instead of `font-lock-face'
  might break something, so a better patch below removes
  the text properties `face info-index-match' from the Info buffer

This is why I posted a better patch.  But please give me more time
to test the second better patch, I'm not yet sure how well it works now.