ID 384327 - Extrusion operations slow down on meshes with high polycounts.

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Problem summary
Extrusion operations slow down on meshes with high polycounts. 

Customer reported version
modo.12.2v1

Customer reported platform
windows10

Steps to reproduce
1) Open Modo.
2) Select File > Open and open the attached scene.
3) Press "3" to enter polygon selection mode.
4) Left-click select the top polygon of the cube.
5) Press "Shift + X" to enable the extrude tool, then left-click drag the polygon from step 4.
Result: Modo will lag/stutter until the left mouse button is released.

Workaround
Unknown.

Reproduced by support
This bug has been reproduced in:
12.2v1 - Windows 10, OSX 10.13.5
12.1v2 - Windows 10
12.0v1 - Windows 10
11.2v3 - Windows 10
11.2v1 - Windows 10
11.1v1 - Windows 10
11.0v3 - Windows 10
10.2v4 - Windows 10, OSX 10.13.5

Earliest version tested
10.2v4 - Windows 10, OSX 10.13.5 - This issue appears to be in all versions of the product

Expected behaviour
Modo should not slow down when performing simple extrusions in a dense mesh layer.

Actual behaviour
Modo slows down when extruding a single face on a mesh island in a dense mesh item.

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