Snap partially selected structure to an attachment bond when rotated

[AlexanderSavelyev]

Background
When user rotates part of a structure, alignment should be done due to a attachment bond(s) (bond which is connected to selected structure)

Solution
Create snap positions for a bond and highlight the snaps according to the following rules

• if there is 1 bond attached - then create 90, 120 and 180 angles snaps. Angle should appear when position is close to the predifined angle
• If there are 2+ bonds then create a snap which divides angle by two between any two bonds near the current position

See screenshots

[PetrKurkin]

Flow for the 1 bond scenario. We move the handle counterclockwise, see 90 degrees angle prompt first, snaps to 120 degrees, and move further to 180 degrees.

90 degrees snap. When highlighted in blue, the bond thickness multiplies by 1.5.

Flow for 2+ bonds scenario. Moving counterclockwise we see a prompt for the bisector, then snap to it.

Bisector snap