Fix ISE when trying to show prompt while it's dismissing

[SUPERCILEX]

Similar to #87, but this time the ViewGroup would blow up saying the prompt view was already added. This PR hardens the show() method even further to reset the prompt if it's currently dismissing.

In addition, it removes broken onAnimationCancel methods. The animator lifecycle guarantees that onAnimationEnd will be called even if onAnimationCancel is also called.

[codecov-io]

Codecov Report

Merging #89 into master will increase coverage by 0.84%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##             master     #89      +/-   ##
===========================================
+ Coverage     93.56%   94.4%   +0.84%     
- Complexity      309     311       +2     
===========================================
  Files            14      14              
  Lines          1025    1019       -6     
  Branches        117     118       +1     
===========================================
+ Hits            959     962       +3     
+ Misses           39      30       -9     
  Partials         27      27

Impacted Files	Coverage Δ	Complexity Δ
...terialtaptargetprompt/MaterialTapTargetPrompt.java	86.94% <100%> (+2.76%)	32 <0> (+2)	⬆️

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[sjwall]

Hey, thanks for your work and the PR. I haven't had chance to review it yet but will do tomorrow

[SUPERCILEX]

NP!

[sjwall]

Changes look good. Thanks again for your work! Changes have been released in v2.4.1

[SUPERCILEX]

Awesome, thanks!