Fixes#11873 this was the primary goal of these changes
Fixes (partially) #11874 the parts of a polyline are combined as a
compound object (shape) but it would be preferable for them to be made
into a wire (if possible)
Fixes#11872 Objects in a block definition are now kept separately
until the block is inserted, in which case the inserted objects are
subject to all the other options regarding combining.
Fixes (partially, review required) #11871 Text and dimensions are now
kept as part of the block definition and are placed in the drawing when
the block is inserted but this code has not been extensively tested.
Affects #11875, custom types are not made, but the labels now reflect
the object types rather than all being "Shapennn"
This leaves the importer options handling in a bit of a mess that needs
cleanup eventually, but this can be a new issue.
This includes some importer flags that have no corresponding options
(e.g. import frozen layers), some flags not yet implemented, some
flags not yet even declared in the code because their implementation
is further off (import hatch outlines), and some suggested future
options (import SOLIDs as faces)
Centralize the calculation of the OCS for entities as they're read
from the DXF. Most of the entities don't use this yet, but some of
them roll their own crude Normal Vector handling. Because the new
code takes priority over the old for reading the normal vector, such
code will always see (0, 0, 1) as the extrusion direction.
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