feat(material/stepper): add input for controlling the animation duration

[crisbeto]

Adds a new input called animationDuration that allows users to control the animation duration of a stepper, similarly to other components.

Fixes #17130.

[ivandevp]

I think this PR is duplicated from one I sent before (#17131). Maybe you can merge the one I mentioned and adding the examples as is the only difference I find. What do you think?

[crisbeto]

We probably ended up working on it at the same time. Aside from the example, these changes are mostly just boilerplate. I'm not sure it makes sense to be merging it in two stages.

[mmalerba]

I just reviewed #17131, that one doesn't have examples and this one doesn't have tests. @ivandevp or @crisbeto, does one of you want to make a PR that includes both?

[crisbeto]

I don't mind adding tests, but there isn't that much there to test. We're just passing an input along to @angular/animations.

[ivandevp]

The tests I added was to confirm the default values for the input is working the same as before this new input.

[crisbeto]

Added a test for the logic that adds units if none are set. I don't think it makes sense to be testing default values.

[ngbot]

I see that you just added the pr: merge ready label, but the following checks are still failing:
     conflicts with base branch "master"

If you want your PR to be merged, it has to pass all the CI checks.

If you can't get the PR to a green state due to flakes or broken master, please try rebasing to master and/or restarting the CI job. If that fails and you believe that the issue is not due to your change, please contact the caretaker and ask for help.

[ivandevp]

Is there any plan to merge this soon?

[mmalerba]

I'm getting errors on a few tests that looks like this:

@stepTransition has failed due to:
- Please provide a value for the animation param animationDuration
- The provided timing value " cubic-bezier(0.35, 0, 0.25, 1)" is invalid.

It appears the duration is misisng, but looking at the code in this PR, I don't know how that would happen. Will need to investigate further

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