This is the page anchors equivalent of the char and paragraph anchors code we
already have.

This makes a difference both on initial layout (nice improvements)
and on interactive moving of page anchored shapes.

This commit also fixes the default anchoring properties to be the same as in LO.

This commit also fixes it so the page anchored iages doesn't leave empty rects on
page 1 after reload

BUG: 312193
BUG: 310715
BUG: 312982
REVIEW: 108358