code ligatures not yet working in Windows Terminal (issues in those apps)

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Please comment/upvote these issues to show support of adding dlig to the following apps:

• Windows Terminal: Investigate/implement renderer setting to disable ligatures microsoft/terminal#759

Why use discretionary ligatures?

Short answer: these allow code ligatures in a multi-purpose font, where they should be available but not turned on by default (because many users might not understand or want them).

Other fonts (Hasklig, Fira Code, Cascadia Code) use calt in a way that doesn't really fit the OpenType spec, but which doesn't matter as much in "single-purpose" fonts.

For reference, from the OpenType spec:

standard ligatures "cover the ligatures which the designer/manufacturer judges should be used in normal conditions. Example: The glyph for ffl replaces the sequence of glyphs f f l."

contextual ligatures "Unlike other ligature features, 'clig' specifies the context in which the ligature is recommended. This capability is important in some script designs and for swash ligatures. Example: The glyph for ft replaces the sequence f t in Bickham Script, except when preceded by an ascending letter."

discretionary ligatures "Replaces a sequence of glyphs with a single glyph which is preferred for typographic purposes. This feature covers those ligatures which may be used for special effect, at the user’s preference. Example: The glyph for ct replaces the sequence of glyphs c t"

contextual alternates "In specified situations, replaces default glyphs with alternate forms which provide better joining behavior. Used in script typefaces which are designed to have some or all of their glyphs join. Example: In Caflisch Script, o is replaced by o.alt2 when followed by an ascending letterform."