Grid size controls should have an upper limit based on screen/container size

[hudson-newey]

Currently, the control to change the verification grid size has a fixed maximum of 36.

This is irrespective of the user's screen size and the size of the verification grid container.

This means that users can see and set grid sizes that are unreasonable.
e.g. A mobile user can set a grid size of 36

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To fix this, the dynamic-grid-size.ts class should advertise the maximum number of grid cells that can fit in the verification grid's container.

[hudson-newey]

Included in this issue:
If the grid size is forcefully increased past the screen maximum (by manually overriding the grid-size HTML attribute) we should display a warning that some items have been truncated