Add support for defStyleAttr to LottieAnimationView

[ataulm]

Is your feature request related to a problem? Please describe.

LottieAnimationView provides the 3-arg view constructor, which allows passing a defStyleAttr from a subclass (e.g. MyLoadingSpinnerView), but doesn't use it.

This means that any LottieAnimationView-specific attributes will not be read from a default style.

Describe the solution you'd like

Pass the defStyleAttr to the init function, and pass it when obtaining styled attributes:

private void init(@Nullable AttributeSet attrs, @AttrRes int defStyleAttr) {
    TypedArray ta = getContext().obtainStyledAttributes(attrs, R.styleable.LottieAnimationView, defStyleAttr, 0);
    if (!isInEditMode()) {
        boolean hasRawRes = ta.hasValue(R.styleable.LottieAnimationView_lottie_rawRes);
        ...

Describe alternatives you've considered

Applying the style explicitly in the layout every time:

<MyLoadingSpinnerView
    style="@style/Widget.MyApp.MyLoadingSpinnerView"
    android:layout_width="40dp"
    android:layout_height="40dp" />

Additional context

Happy to do a PR if this issue is accepted!

Lottie is supported and developed on nights and weekends. Please consider sponsoring Lottie to prioritize this issue and help support this issue as well as future investments.

[gpeal]

@ataulm I would accept a PR for this!