Change window type of Media Projection dialog

With the dialog changes of not closing QS, the dialog type needs to
change to present on top of the shade.

This CL changes it to match that of the dialog launched by CastTile.

Fixes: 209532003
Test: manual
Change-Id: I937678a5d8ee91902c324aa063e48610de7b0f74
(cherry picked from commit c5bd57337074eaccfda57a62612c77c26ed71e97)
Merged-In:I937678a5d8ee91902c324aa063e48610de7b0f74