Add et-tailed variant to ampersand

[GreenYun]

• The requested variant shape does not go too far away from Iosevka's design.
• The requested variant does not conflict with any characters in Unicode that Iosevka currently supports.
• At least two monospace/programming fonts, created by different designers, supported the requested variant. Provide images below.

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I was considering that to add et-tailed variant to the ampersand character would help match the styles of lowercase latin letters, like u (toothed, tailed).

The reference image below is from a typeface called "Agave" that providing et-tailed style as the ampersand character.