Re-land: Change mapping of text leaf nodes and line breaks to ATK_ROLE_STATIC

Originally landed: crrev.com/c/1749145
Reverted: crrev.com/c/1751830

The revert was due to Trusty not supporting ATK_ROLE_STATIC. The change
is something which can wait but should be made eventually.

Original commit message:

  Text leaf nodes and line breaks were being exposed as ATK_ROLE_TEXT.
  However, the definition of ATK_ROLE_TEXT is:

    An interactive widget that supports multiple lines of text
    and optionally accepts user input, but whose purpose is not
    to solicit user input.

  In contrast, ATK_ROLE_STATIC is defined as:

    A generic non-container object whose purpose is to display
    a brief amount of information to the user and whose role is
    known by the implementor but lacks semantic value for the user.

  Thus text leaf nodes and line breaks should be exposed with the latter
  role; not the former.

Bug: 984590
Change-Id: I7da4ea79dcac546a96e55d5ef57c9a052e9bd578
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1872409
Auto-Submit: Joanmarie Diggs <jdiggs@igalia.com>
Commit-Queue: Martin Robinson <mrobinson@igalia.com>
Reviewed-by: Martin Robinson <mrobinson@igalia.com>
Cr-Commit-Position: refs/heads/master@{#712495}
196 files changed