refactor(stepper): rework buttons to handle Ivy (#15429)

[crisbeto]

Equivalent of #15429 for the Ivy branch.

In Ivy inheriting host bindings works correctly by merging the two declarations, whereas in ViewEngine the bindings aren't inherited at all. This means that with our current setup the click listener on the buttons will be invoked twice with Ivy.

These changes rework the buttons so that they work both with Ivy and ViewEngine.

[ngbot]

I see that you just added the pr: merge ready label, but the following checks are still failing:
status "ci/circleci: api_golden_checks" is failing
status "ci/circleci: bazel_build_test" is failing
status "ci/circleci: build_release_packages" is failing
status "ci/circleci: e2e_tests" is failing
status "ci/circleci: lint" is failing
status "ci/circleci: prerender_build" is failing
status "ci/circleci: tests_browserstack" is failing
status "ci/circleci: tests_local_browsers" is failing
status "ci/circleci: tests_saucelabs" is failing
missing required labels: target: *

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