Fix: Expanding the Texture Atlas Limit for Fonts with Large Character Sets

[rustbasic]

When using fonts with an average of 50,000 characters, 'epaint texture atlas overflowed!' may be printed and cause problems. It is necessary to expand the max value related to texture.

• Closes #5256

[github-actions[bot]]

Preview available at https://egui-pr-preview.github.io/pr/5257-patch138 Note that it might take a couple seconds for the update to show up after the preview_build workflow has completed.