Remove non-contiguous parts of a grid

[veenstrajelmer]

Is your feature request related to a problem? Please describe.
When generating a grid and deleting landward parts with a polygon, sometimes this results in "loose" parts of a grids. These non-contiguous parts could be lakes or just a result of a coarse polygon, but since they have no connection to the model, they can be removed. This also results in contiguous partitioning by FM, which is convenient.

Describe the solution you'd like
New function to delete non-contiguous parts of a grid. Maybe also an algorithm that efficiently checks if all cells are connected to each other.

[veenstrajelmer]

Possible with xugrid, which might be a working approach:

import xugrid as xu
grid = xu_grid_uds.grid
uda = xu.UgridDataArray(
    xr.DataArray(np.ones(grid.node_face_connectivity.shape[0]), dims=["face"]), grid
)
labels = uda.ugrid.connected_components()
counts = labels.groupby(labels).count()
most_frequent_label = counts["group"][counts.argmax()].item()
labels = labels.where(labels == most_frequent_label, drop=True)

fig, ax = plt.subplots(figsize=figsize)
labels.ugrid.plot(cmap="jet")

https://deltares.github.io/xugrid/examples/connectivity.html#connected-components

Applied to a grid, it results in the desired behaviour

Nevertheless, we might still want to implement it also in meshkernel.