Fix: cassowary/layouts: add extra constraints for fixing Min(v)/Max(v) combination.

[orhun]

Upstream: #647

Description

These added weak constraints prevent zero width/height widgets when combining Min(v)/Max(v) together in a chunk.

The UI will now reflow correctly when (re)sizing, gracefully preserving Max(v) constraints as much as possible.

This fixes the root cause of the issues identified in:
fdehau/tui-rs#39
fdehau/tui-rs#420
(amongst probably similar reports).

Testing guidelines

Combine Min(v) and Max(v) layout constraints in a chunk.

...
        let chunks = layout::Layout::default()
            .direction(layout::Direction::Horizontal)
            .constraints([Constraint::Min(50), Constraint::Max(25)])
            .split(frame.size());
...

Use any other combination, including Percentage/Ratio/Length with Min/Max.

Resize the window width/height to investigate how the two constraints are now satisfied without 'freaking out' and generating zero-width/height widgets. If all Min(v)/Max(v) constraints cannot be satisfied, they will gracefully degrade.

Checklist

• I have read the contributing guidelines.
• I have added relevant tests.
• I have documented all new additions.

[sayanarijit]

Tested locally. Looks good.

[orhun]

LGTM! (cannot approve my own PR)