Fix 'cross-section' style of Channel layer for tabulated profiles

[leendertvanwolfswinkel]

The size of the marker should be data-defined and equal to the max width of the cross section. This max width is currently already calculated using the custom function cross_section_label() My suggestion is to add and expose custom functions cross_section_max_height() and cross_section_max_width() that can be used in stylings.

[leendertvanwolfswinkel]

Also make these functions deal with the new cross section shapes (YZ, Inverted Egg, Closed Rectangle)

[ldebek]

@leendertvanwolfswinkel What are the desired label formats for the shapres mentioned above?

[leendertvanwolfswinkel]

0: Closed rectangle w: {cross_section_width} h: {cross_section_height}

7: YZ w: {max y} h: {max z}

8: Inverted egg w: {cross_section_width} h: {1.5*cross_section_width}

[ldebek]

@leendertvanwolfswinkel Changes available for testing on branch: xs_labels_new_shapes_update

[leendertvanwolfswinkel]

The label for 'Open rectangle' should only include the width:

1: Open rectangle w: {cross_section_width}

Please group the custom QGIS Expressions in a group called '3Di' instead of 'Custom' if this is possible

[ldebek]

@leendertvanwolfswinkel Requested changes applied.