Impeller engine gives errors for intro lottie animation

[w-ensink]

In #289 we have disabled the Impeller rendering engine on iOS due to an issue with the yivi intro lottie animation. When the animation zoomed in it would show the following error repeatedly:

[ERROR:flutter/impeller/base/validation.cc(59)] Break on 'ImpellerValidationBreak' to inspect point of failure: Subpass render target is invalid.
[ERROR:flutter/impeller/base/validation.cc(59)] Break on 'ImpellerValidationBreak' to inspect point of failure: Requested texture size (9620, 3359) exceeds maximum supported size of (8192, 8192)
[ERROR:flutter/impeller/base/validation.cc(59)] Break on 'ImpellerValidationBreak' to inspect point of failure: Could not create multisample color texture.
[ERROR:flutter/impeller/base/validation.cc(59)] Break on 'ImpellerValidationBreak' to inspect point of failure: Render target does not have color attachment at index 0.
[ERROR:flutter/impeller/base/validation.cc(59)] Break on 'ImpellerValidationBreak' to inspect point of failure: Render target does not have color attachment at index 0.
[ERROR:flutter/impeller/base/validation.cc(59)] Break on 'ImpellerValidationBreak' to inspect point of failure: Subpass render target is invalid.

Impeller is the new default rendering engine for Flutter on iOS and it's unclear for how long the older Skia engine will remain supported. At some point Impeller will therefore have to be switched back on, hopefully when the issue has been resolved by the Flutter team.

To test with the impeller engine enabled, you can run with flutter run --enable-impeller. To re-enable impeller permanently, you need to edit ios/Runner/Info.plist and remove the following:

<key>FLTEnableImpeller</key>
<false/>