Fix broken flyout layout due to RTD addons upgrade

[r0qs]

RTD is no longer injecting certain HTML elements, such as the flyout menu, and they are replacing these components with addons (see: readthedocs/readthedocs.org#11474). Unfortunately, addons does not work out-of-the-box with the customizations we have implemented - specifically, having a fixed flyout menu at the bottom of the sidebar in our docs.

The issue is because we explicitly use certain CSS selectors (e.g., .rst-versions) to determine where to place the flyout menu, and the current code relied on such selector and didn't properly handle cases where such selector would not be present, breaking the layout with a type error since rstVersions is null. And the same applies for other selectors that are removed in this PR.

solidity/docs/_static/js/initialize.js

Line 26 in 4ab3e36

rstVersions.remove();

The addons are enabled by default in the RTD dashboard, and it appears that we cannot disable them, see: readthedocs/readthedocs.org#11474 (comment).

You can see the docs of this PR here: https://docs.soliditylang.org/en/rtd-docs-workaround/
And some old broken version here: https://docs.soliditylang.org/en/v0.8.27/ (check the browser console for the error)

Note that this PR does not resolve the layout issues for older versions; it only applies to new releases. To keep older versions somewhat usable, the Flyout option should be enabled in the RTD dashboard.

The PR also introduces checks to safely access properties or call methods on potentially null or undefined objects.

[ekpyron]

Assuming that we'd notice it the input[name=mode] things weren't gone in some cases, this is probably safe to merge

Rodrigo still wanted to look into some other stuff, so I'm dismissing the approval for now.

[ekpyron]

I guess the regexes could be combined into one or two in principle, but also fine with me for now

[ekpyron]

The docs ci build failing is an issue, though :-)

[ekpyron]

For half of this I'm not 100% clear on why it becomes necessary, but this seems to improve the situation at least, so we can merge and take it from there.