Add support for bubble enhanced P2 element in 2D

The conforming Crouzeix-Raviart element

$P_2^+-P_1^\text{disc}$

for triangles in 2D employs for the velocity component continuous quadratic Lagrange elements extended by a cubic bubble function. This MR adds to HOG support for this

P_2^+

part.

added new feature label

requested review from @he66coqe

assigned to @mohr

added 1 commit

• aacf835a - Do not try to generate 3D forms for P2PlusBubble element, yet.

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added 1 commit

• c5d1a348 - Make code for AffineMap2D more elegant and expressive

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approved this merge request

resolved all threads

merged

mentioned in commit 5eb739da

mentioned in issue #49