Merge branch 'master' into soc-2021-knife-tools

Fix: Knife keymap failed unit test

Knife: Replaced object bases array with object array

The Base structs were only ever used to retrieve the Object struct and so could be replaced.

Merge branch 'master' into soc-2021-knife-tools

Fix: Warning caused by setting enum value to bool

Knife: Better multi-object edit mode

The knife tool can now make cuts in multi-object edit mode which cross over multiple objects and go from the geometry of one object to multiple others.

Previously, object switching functionality was implemented but this proved insufficient to achieve the functionality contained within this patch. Instead, the dependence on a singular Object and BMEditMesh stored in the KnifeTool_OpData struct needed to be entirely removed.

This has resulted in a lot of passing around of Object pointers which could potentially be simplified using a map of some kind in the future. For now it works well.

Knife: Moved code to world space

This patch migrates the knife tool code to use world space coordinates instead of object space.
This is required to implement the ability to cut across multiple objects at once and the ability to use the geometry of other objects as a cutting reference.

This introduces precision errors for objects with very large scale or location, however it may be possible to add a switch between world space and object space coordinates depending on whether the user is in multi-object edit mode or not.

Knife: Cut along edges to reposition cut start more easily

After receiving feedback on devtalk, users expressed they wished to be able to cut along an edge so they could make further cuts from a new position along the edge.
This also adds the potential to implement snapping to a given distance along an edge.

Fix: Knife cut vertex sometimes placed in space

When using relative constrained angle mode along an edge which has a face hidden from view, if a cut is added it can sometimes place the previous cut vertex in space, away from the edge.
This was caused by knife_snap_edge_constrained not working correctly when a cut is constrained along the edge it was started from.

Fixed by adding a quick check.

Fix: Function parameters changed

The parameters to ED_transform_calc_orientation_from_type_ex needed to be changed after a merge from master.
This fixed axis constraint for the knife tool.

Merge branch 'master' into soc-2021-knife-tools

Knife: Setting to toggle X-Ray

Knife tool xray (depth testing) was previously only toggle-able by the 'V' modal key.
This patch exposes an RNA boolean in the knife tool settings for toggling xray.

Merge branch 'master' into soc-2021-knife-tools

Merge branch 'master' into soc-2021-knife-tools

Knife: Enter angle snapping increment with numpad multiple times

Entering a value for angle snapping increment using the numpad was only allowed once.
To re-enter a value angle snapping had to be toggled off and back on.
Now you can repeatedly re-enter values, except values cannot have decimal points.
If a more precise angle is required, the knife tool settings exposes the angle snapping increment.

Knife: Renamed depth check to x-ray

The name depth check was confusing some users. Renaming it to x-ray makes more sense.

Knife: Rename local angle snapping to relative angle snapping

Fix: Knife relative edge for snapping drawn with object space coords

It should've been drawn with world space coords.

Cleanup: Moved Knife axis colors into KnifeColors struct

Cleanup: Cpp style comments to C style