Auto-resizing and vertical alignment require a non-empty text box. But
currently, the presence of the text box is used to discriminate between
point text [1] and paragraph text [2].
In order to support auto-scaling and v-alignment for point text, we must
decouple the text mode encoding from the text box:
* introduce and explicit LinebreakPolicy property for skottie::Shaper,
and use it to control line breaking instead of the text box presence
* by default, the line breaking policy is initialized per existing
AE/BM semantics: non-empty text box -> paragraph mode,
empty box -> point mode
* the policy can be overridden via the PropertyObserver APIs to enable
point mode auto-resizing and vertical alignment
[1] https://helpx.adobe.com/after-effects/using/creating-editing-text-layers.html#enter_point_text
[2] https://helpx.adobe.com/after-effects/using/creating-editing-text-layers.html#enter_paragraph_text
Change-Id: I007144283a31a2faa579d7eec82af72af3d540cb
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/321788
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Florin Malita <fmalita@google.com>
