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'

Demo Video:

Code used for visual testing

const data = Array.from({ length: 20 }, (_, i) => ({
  x: [1, 2, 3],
  y: [40 + i, 50 + i, 60 + i],
  name: `long trace name #${i}`,
  type: "scatter"
}));

const layout = {
  width: 1000,
  height: 400,
  margin: {
    l: 0,
    t: 120,
    r: 0,
    b: 120,
    autoexpand: false
  },
  legend: {
    orientation: "v",
    xref: "container",
    yref: "container",
    xanchor: "left",
    yanchor: "top",
    x: 0.05,
    y: 0.25,
    bgcolor: "lightgrey"
  }
};

Plotly.newPlot("myDiv", data, layout);

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'