Some BarPlot Fixes

[freddyaboulton]

Description

Closes: #4530 Closes: #4529

To test, run native_plots in dark mode and note that the label for the bar plot does not show up and that the plot text is white when you select grouped or grouped-horizontal int the bar plot tab.

Checklist:

• I have performed a self-review of my own code
• I have added a short summary of my change to the CHANGELOG.md
• My code follows the style guidelines of this project
• I have commented my code in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

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[gradio-pr-bot]

All the demos for this PR have been deployed at https://huggingface.co/spaces/gradio-pr-deploys/pr-4531-all-demos

[abidlabs]

Can confirm the fixes, thank you @freddyaboulton!

[freddyaboulton]

Thanks @abidlabs !