2Geom sync - initial commit

Update to experimental r13565

Properly allow effect stacking with knotholders (and add extra LPE functionality)

const ....

UI uniformisation

Fix "shift disables snapping" for LPEs and for editing objects

Removed unneeded header style filename #defines

Removed outdated classes. Pruned header to not introduce extraneous includes.

Adding base configurable sizing of controls/handles.

cleanup knotholder code for LPEs

turn SPPath into a class, and add some methods...

remove many needless references to n-art-bpath.h

2geomify a lot of NR::Points to Geom::Point

Make LPE knotholder handles snap

Rename isLPEParam() to isDeletable(), create new class LPEKnotHolderEntity and make inheritance from it a bit less clumsy

Fix wrong descriptions

First step towards making helper paths for LPE items work better

whitespace

warning cleanup

Get rid of get_bpath() in lpe-tangent_to_curve.cpp

Write all effect parameters to SVG when a LPE knotholder handle is ungrabbed

Re-add two handles for PerpBisector LPE (we don't add the other two because they would duplicate the path's own handles and the correct solution would be to allow knotholders and nodepaths at the same time). Put the KnotHolderEntity classes into their own namespaces to avoid clashes.

Better way to add LPE knotholder handles; now it happens semi-automatically in a similar way as adding LPE parameters.

Make knotholders for LPE items finally work; each effect can now overload the addKnotHolderHandles() method to add handles which control its parameters. There is now also a virtual onKnotUngrabbed() method for each knotholder entity which can be used to do cleanup tasks (for LPE parameters it currently writes the value to SVG, although this should probably happen automatically)

set eol-style:native for recently added files

LPE STACKING! (many thanks to the french students who made this.)

Add possibility to let the 'tangent' have a fixed angle relative to the curve

Add handles to adapt tangent length

Forgot to add two files in commit #18667. Sorry for breaking the build for a minute!