[ShapeableImageView] Fix multiple contentPadding issues

[jpmcosta]

Solution

Closes #2063.

Should fix the following contentPadding issues:

• contentPadding getters returning outdated values when app:contentPaddingStart or app:contentPaddingEnd are defined in xml;
• contentPadding being applied twice, if setContentPadding or setContentPaddingRelative are called before the view is measured;
  • in this case, the shape mask is also affected to have padding even if only contentPadding is defined.

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