fix(tooltip): render style values in ngOnInit instead of the constructor

[matsko]

Due to changes in Angular it's not logical to change style values
directly within a constructor. This should be done instead within
the ngOnInit lifecycle hook.

This patch changes this behavior for the ToolTip component.

[crisbeto]

LGTM once the CI is sorted out.

[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
     missing required labels: target: *

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