Not all ligatures are rendered correctly [webgl]

[dileep-kishore]

Oni Version: v0.3.7-beta3
Neovim Version (Linux only): v0.3.1
Operating System: Manjaro Linux

Issue:
Some ligatures are not rendered. Eg: __init__

Font used: Fira Code
Renderer: webgl

Expected behavior:

It looks like this feature was implemented in #2560. This could be a duplicate of #2610 .

[oni-bot]

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[CrossR]

@cryza should this be covered by the fix up PR you did? (#2619)