alt attribute should contain the Unicode emoji

[Crissov]

The alt attribute should contain the Unicode emoji and only that, the current descriptive text may be used in the title attribute.

<g-emoji fallback-src="t-rex.png" alias="T-Rex">🦖</g-emoji>

currently yields

<g-emoji fallback-src="t-rex.png" alias="T-Rex">
  <img class="emoji" alt="T-Rex" height="20" width="20" src="t-rex.png">
</g-emoji>

but should result in

<g-emoji fallback-src="t-rex.png" alias="T-Rex">
  <img class="emoji" alt="🦖" title="T-Rex" height="20" width="20" src="t-rex.png">
</g-emoji>

I noticed this problem when trying to copy and paste rendered comments where I did not get the emoji as expected even though the other environment supported emojis.