Assets: improve colors performance

[djbe]

Fixes #578.

To use lazy var, had to switch to final class with our own init. This is better than parsing the color during init as we can keep the @availability annotation for the color property.

[SwiftGen-Eve]

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[djbe]

Rebased with changes from feedback.

[AliSoftware]

LGTM but I'd love for @eaigner to weight in and confirm it fixes the performance issue they observed.

[eaigner]

While I can't speak to the performance aspect right now (the code was changed since i reported the issue), the stencil works.

[djbe]

Could you try it with your local generated code, replacing the struct with a final class, and the computed var by a lazy var?

[eaigner]

I have. But I did not benchmark performance. But since its lazy now, should not be a problem, right?

[djbe]

I think it's safe to assume that the lazy vars solve the issue. Will merge this PR this evening unless there's more feedback.

[eaigner]

When is 6.2 scheduled to release? Would be nice to have this out there. It's almost 2 months now.

[djbe]

I've been swamped with work these last few weeks, big upcoming release at work.

TBH, things are ready for release, just some final checks and changelog/docs updates (see #621). Maybe this weekend, but I can't promise anything.