Fix legend container overflow

[attatrol]

Description

Fixes maximum height calculation for legends anchored to the container (yref: "container"). Previously, legends would overflow outside the available container space. This fix ensures that when a legend is positioned relative to the container, its maximum height is constrained to the available space based on the y position and yanchor settings.

Resolves #7072

Changes

• Updated computeLegendDimensions function in src/components/legend/draw.js to calculate and constrain maxheight when yref === 'container'
• Added test mock legend_overflow_height.json to verify the bug fix

Demo Video:

Before:

Screen.Recording.2025-10-27.at.11.30.24.PM.mov

After:

Screen.Recording.2025-10-27.at.11.30.52.PM.mov

Testing

• Start the dev dashboard with npm start
• Search for the legend_overflow_height mock
• Scroll vertically in the legend component
• Check that the legend respects the boundaries of the container and doesn't overflow outside the available space

[alexshoe]

@emilykl @camdecoster
Fixed the merge conflict for this one and made some minor changes for readability + reducing redundancy.
Filled in the description too so that it matches the standard.

[emilykl]

I'm pretty sure you could avoid the yref === 'paper' check here by just setting useFullLayoutHeight to false inside the else case

[emilykl]

In fact I think you need to do that, because otherwise useFullLayoutHeight is undefined when yref is not 'paper'