Fix minangle forwarding to TetGen and adjust default value

[pjaap]

We need an additional / after the q flag, as stated in 10.20347/WIAS.TECHREPORT.13 in section 4.2.3.

The old default of 20 seems to large for me. I adjusted it to 10 for TetGen.

Small demo code generating two unit cubes with different maxvolume constains:

function foogrid(;
        h = 1.0,
        H = 2.0
    )

    builder = SimplexGridBuilder(; Generator = TetGen)

    # bottom
    p01 = point!(builder, 0, 0, 0)
    p02 = point!(builder, 1, 0, 0)
    p03 = point!(builder, 1, 1, 0)
    p04 = point!(builder, 0, 1, 0)
    facet!(builder, p01, p02, p03, p04)

    # central intersection
    p11 = point!(builder, 0, 0, 1)
    p12 = point!(builder, 1, 0, 1)
    p13 = point!(builder, 1, 1, 1)
    p14 = point!(builder, 0, 1, 1)
    facet!(builder, p11, p12, p13, p14)

    # top
    p21 = point!(builder, 0, 0, 2)
    p22 = point!(builder, 1, 0, 2)
    p23 = point!(builder, 1, 1, 2)
    p24 = point!(builder, 0, 1, 2)
    facet!(builder, p21, p22, p23, p24)


    # front face
    facet!(builder, p01, p02, p12, p11)
    facet!(builder, p11, p12, p22, p21)

    # right face
    facet!(builder, p02, p03, p13, p12)
    facet!(builder, p12, p13, p23, p22)

    # back face
    facet!(builder, p03, p04, p14, p13)
    facet!(builder, p13, p14, p24, p23)

    # left face
    facet!(builder, p04, p01, p11, p14)
    facet!(builder, p14, p11, p21, p24)


    # upper cell region
    cellregion!(builder, 1)
    maxvolume!(builder, h)
    regionpoint!(builder, 0.5, 0.5, 1.5)

    # lower cell region
    cellregion!(builder, 2)
    maxvolume!(builder, H)
    regionpoint!(builder, 0.5, 0.5, 0.5)

    options!(builder; minangle = 10)

    return simplexgrid(builder)
end

gridplot(foogrid(h = 0.0001, H=1), Plotter=GLMakie, yplanes = [0.5], scene3d = :LScene)

This was the situation before, very poor quality, angle was not respected

This is the situation with minangle = 20

This is the situation with minangle = 10

[pjaap]

Tests need adjustments to the new meshing. Will change that after the new default etc is approved

[pjaap]

Test values are updated. Is ready for final review and merge

[j-fu]

LGTM