Use generated functions for logic AXNodeObject::Orientation()

* Use RoleSupportsAriaOrientation() to determine if a value should be
  exposed (after special-casing comboboxes to prevent test failure).
* Use GetImplicitAriaOrientation(RoleValue()) instead of the hard-coded
  defaults.

Change-Id: I80cfdd7db5a6569f89876a7a9f560bedd6022a57
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7032171
Reviewed-by: David Tseng <dtseng@chromium.org>
Commit-Queue: Joanmarie Diggs <jdiggs@igalia.com>
Cr-Commit-Position: refs/heads/main@{#1537462}