Variant: colon vertically centered

[notpeter]

• 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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The vertical placement of : (and related ligatures: ::, :::, etc) varies depending on context:

1. Colon sits on the baseline or
2. Colon sits vertically centered on the median

Specifically typing ::< character-by-character (used for the turbo fish operator in rust) results in the three distinct positions of the colon. The horizontal movement when making the :: (expected ligature behavior) and vertical movement when typing the subsequent character. I find the vertical movement extremely distracting. It occurs when a : is followed by any of <>=-+ (not just <).

Depending on context, the colon(s) move up or down when the next character is typed. Here is an animated example demonstrating these behaviors:

Proposal: add variants for the colon character : so a vertically centered placement can be enabled as a default. This currently possible with the * character, but not for :. Such a variant would also make it possible to avoid two successive :: within a single call being displayed at different heights (see: mem::size_of::<u8> in the gif above.)

I observed this behavior in the Zed editor which includes an Iosevka customization Zed Mono. Here is the associated custom build config.

[glepnir]

I got same problem . reprocue can by simply using a rust code like std::O