fix(panel): resolve animation issues

[Splaktar]

PR Checklist

Please check that your PR fulfills the following requirements:

• The commit message follows our guidelines
• Tests for the changes have been added or this is not a bug fix / enhancement
• Docs have been added, updated, or were not required

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Enhancement
[ ] Documentation content changes
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

1. panels that animate in aren't shown on screen
2. panels that are reused, accumulate transforms causing strange, compounding issues

Issue Number:
FIxes #11946

What is the new behavior?

1. remove md-panel-offscreen from innerWrapper in _updatePosition() if init is true
2. remove the inline transforms after the close animation runs so that reused panels don't accumulate transforms

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

I'll merge this to master and then cherry pick it to the 1.1.x branch.

[Splaktar]

@oliversalzburg PTAL

[mmalerba]

LGTM

[oliversalzburg]

It looks pretty good to me, although I'm again unable to easily test this 😭 Given that the transform is now removed, I have high hopes for this change. I suspected code to achieve that existed previously and was simply not triggered for some reason. If we can get this merged, I'll test a build from the bower repo ASAP.