[Webview-FillDialog Support] Fix autofill framework issue found when testing webView prorotype

There are two issues I found:

1. Instead of SparseArray.indexOf(i), framework should use SparseArray.keyOf(i) to get the virtual id for virtual views that Chrome passed in.

2. Framework should ignore case when checking whether view's autofill hints is in fill dialog supported hints. In the webview prototype, Chrome is passing "PASSWORD" as autofill hints

Also I found it's easy to create null pointer exception when referencing
AutofillHints in notifyViewReadyInner(). It's not obvious that this
array could be null also. Annotated it with @Nullable to make it obvious.

Bug:b/299532529
Test: atest CtsAutoFillServiceTestCases

Change-Id: Ie1ed6f0fbe806826a1844d85a74767ca946e55b8