The emoji_icon helper used to display the award emoji in Issue and
Merge Request views. By default the spritesheet is used, but passing
`sprite: false` to the `emoji_icon` helper makes the emoji render as
separate images.

For award emoji displayed by default (e.g. thumbs-up, thumbs-down, and
any that have been awarded to the issue/MR) the independent images are
used. Only when the full emoji menu is opened does the full spritesheet
load.

On a normal issue this change decreases the page load by 670KB or 250KB
depending on pixel density.

Resolves #14334.