Clean up Path tool related code and fix bugs in several cases

[4adex]

Solved these following minor regressions in the path tool -

• Ctrl A in path tool, should select all segments also if segment select mode is enabled. (https://discord.com/channels/731730685944922173/881073965047636018/1406378997830521102)
• The overlay of hovering segment remains after deleting the segment in segment select mode. (https://discord.com/channels/731730685944922173/881073965047636018/1406376716657754263)
• Fix the flawed implementation of select_points_by_manipulator_id and changed it from every location. (https://discord.com/channels/731730685944922173/881073965047636018/1399272679952875632)
• Path tool overlays (specifically the three modes introduced in Add Pen and Path tool modes to avoid showing all handles #2264) were erroneously shown when there were duplicate layers, that has been fixed now by passing LayerNodeIdentifier along with the PointId for uniqueness of point.
• Flip Smooth Sharp had bloated code from previous implementation which used to check closest point and then change it to smooth or sharp, it was later changed to flipping for all selected points (Make the Path tool support multi-point conversion between smooth/sharp on double-click #2498)
• Flip smooth sharp didn't worked for points of other layers which are also in the selection (it does now).
• Vector mesh support for Ctrl + J join path feature, if vector mesh enabled, can join non terminal points also.