Symbols for blending variables (jacobian, inverse and determinant)
As we discussed, here I have attempted to add blending jacobian symbols which significantly speeds up the code generation time (definitely needed for hessians).
New functions which enables the symbols for blending are added in the symbolizer. These are then replaced in the quadrature loop with quadrature point dependent symbols, which are then again replaced in the innermost loop later in code generation with a function similar to the affine jacobian substitution.
I have tested this in the diffusion form and seems to work with a simple integration test.
If this method is fine, then I can change all forms according to this.