Forward BrowserAccessibility get_accState to AXPlatformNode.

This is another migration from BrowserAccessibility to AXPlatformNodeWin.
In this installment, we're converting get_accState. This one is mostly
straightforward. The one gotcha is that there are some types that need
to be explictly marked as focusable if they are selectable.

BUG=703369

Review-Url: https://codereview.chromium.org/2913553002
Cr-Commit-Position: refs/heads/master@{#478110}
12 files changed