Replace PNG with SVG icons in docs

[pavithraes]

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• issues: fixes [DOCS] Update docs pages with new SVG icons #14521
• tests added / passed
• release document entry (if new feature or API change)

Blocked on: #14563

[pavithraes]

This is to ensure the icons in the docs directory are in sync with the ones in bokehjs.

I'm not sure if this is the best approach, but it's the one I was able to test & get working.
While we can copy the icons directly to the build dir, I wasn't able to link to those from the .rst files -- they seem to need relative links or full URLs. Hence, copying files to the source dir. Please let me know if there is an alternative.

[mattpap]

/home/runner/miniconda3/envs/bk-test/lib/python3.10/site-packages/bokeh/models/tools.py:docstring of bokeh.models.tools.PolyEditTool:27: WARNING: image file not readable: _images/icons/poly-edit.svg [image.not_readable]
/home/runner/miniconda3/envs/bk-test/lib/python3.10/site-packages/bokeh/models/tools.py:docstring of bokeh.models.tools.PolyEditTool:27: WARNING: image file not readable: _images/icons/poly-edit.svg [image.not_readable]
/home/runner/work/bokeh/bokeh/docs/bokeh/source/docs/user_guide/interaction/tools.rst:1200: WARNING: image file not readable: _images/hover.svg [image.not_readable]
/home/runner/work/bokeh/bokeh/docs/bokeh/source/docs/user_guide/interaction/tools.rst:1244: WARNING: image file not readable: _images/icons/poly-edit.svg [image.not_readable]
/home/runner/work/bokeh/bokeh/docs/bokeh/source/docs/user_guide/interaction/tools.rst:1200: WARNING: image file not readable: _images/hover.svg [image.not_readable]
/home/runner/work/bokeh/bokeh/docs/bokeh/source/docs/user_guide/interaction/tools.rst:1244: WARNING: image file not readable: _images/icons/poly-edit.svg [image.not_readable]

[pavithraes]

For poly-edit.svg, I think it should be resolved after #14563 is merged. (I tested it locally)

[mattpap]

@pavithraes, what was the reason to commit copied SVG icons? I removed them in 29119c0. Documentation build fails due to unrelated reasons already fixed in branch-3.8.

[pavithraes]

what was the reason to commit copied SVG icons?

The icons were not required and shouldn't have been included. Thanks for also updating the gitignore file!

[github-actions]

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