Updates to 2D polygonal transformation

[nselliott]

This brings in updated features to the to_polygonal transformation of 2D structured AMR meshes:

• Handles block rotations
• Fixes case where a corner of a fine domain is not a vertex on the coarse mesh
• Includes fields in the transformation, including communication of vertex field values from fine domains to coarse domains at hanging vertices, matching the communication of coordinate positions at those same vertices.

[cyrush]

@nselliott this looks good.

More comments in conduit_blueprint_mpi_mesh about the cases would help our future selves.

Do you think we should we wire up the more complex bent grid example as part of this PR, or in a future PR (future PR is fine by me)

[nselliott]

@nselliott this looks good.

More comments in conduit_blueprint_mpi_mesh about the cases would help our future selves.

Do you think we should we wire up the more complex bent grid example as part of this PR, or in a future PR (future PR is fine by me)

@cyrush I think we can do the bent grid in the next PR.