Increase size of legend in Legend guide example

[saranti]

PR summary

While I was looking at issue #8789, I saw that the legend in the example under https://matplotlib.org/devdocs/users/explain/axes/legend_guide.html#legend-handlers was pretty cramped and could look better with an increase in the length of the handles.

Before:

After:

This also looks like the right spot to document this feature (which is what that issue is about). More could be said about it, maybe with its own example and heading.

PR checklist

• "closes #0000" is in the body of the PR description to link the related issue
• new and changed code is tested
• Plotting related features are demonstrated in an example
• New Features and API Changes are noted with a directive and release note
• Documentation complies with general and docstring guidelines

[story645]

Can you add a comment or half a sentence on what handle length does?

[saranti]

Is that enough?

[story645]

I think I'm confused on what handlelength does vs numpoints here

[saranti]

Numpoints adds the 4 dots to the legend entry and handlelength just increases the length of the handles.

The docs say "Line 1" now has 4 marker points, where "Line 2" has 2 (the default).

(It's really 1 though 🤔)

[saranti]

Should this also close issue #8789?