[animations] Adds ability to show a translucent modal route

[matheuslutero]

Currently the _OpenContainerRoute.opaque property is fixed to true, this change will add the ability to set this value to false if needed. This way we will be able to push a translucent route.

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[goderbauer]

I am curious to see what visual effect you are going for with this option. Do you have an example of how you intent to use this? The open container animation was very much designed with the expectation that the opened container would cover the entire old content...

[stuartmorgan-g]

[x] I listed at least one issue that this PR fixes in the description above.

@matheuslutero Could you file a proposal issue with a more detailed use case, to answer the question above, and link it here?

[matheuslutero]

Hi folks, sorry for the late reply. I'll have some time next weekend, so I will attach an example of this usage here.

[stuartmorgan-g]

I will attach an example of this usage here.

Please file a proposal issue, as requested above and described here, rather that making the proposal in the PR.

[stuartmorgan-g]

@matheuslutero Is the proposal discussed above still something you are planning on moving forward with?

Marking as a draft for now since there's not yet sufficient context for a code review.

[goderbauer]

(triage) I am going to close this one since there was no follow-up. If you find the time to work on this again please feel free to reopen the PR.