New AccessibilityNodeInfo fields for tracking collection counts and unimportant views

Raw adapter counts when surfaced to users can be misleading if some of the
items are unimportant for accessibility. This has traditionally been a rich
source of accessibility bugs (see b/137113167 and 9 duplicates).

We handled this issue previously by removing Collection[Item]Info from
commonly used collections; We reinstated Collection[Item]Info recently
because its absence blocked the development of other features important
to the platform. This effectively reopens all bugs related to collection
counts previously fixed by removing Collection[Item]Info.

This commit provides a way for developers to specify the collection
count and the number of important views (they can do this via an
AccessibilityDelegate). Accessibility services like Talkback can then
surface the correct count information to users.

The new fields also make it possible to describe the size of staggered
grids, which do not neatly conform to row/column semantics.

Bug: 266133760
Bug: 137113167
Bug: 269756921

Test: See AccessibilityNodeInfo_CollectionInfoTest.java

Change-Id: I86c9c793bb43fd247db13641c2bf1eb9ff24d09c