Resolve collisions in reference anchors added for methods

[YuriSizov]

While the anchors themselves were sufficiently unique, when converted to HTML all underscore characters are replaced. This created collisions between, say, Object._get and Object.get, where the latter would get a generic unique anchor identifier, e.g. id1.

You can test this yourself in the current version of the online documentation: https://docs.godotengine.org/en/stable/classes/class_object.html

Now, this change will break existing links in the online docs, which need to be fixed manually after the class reference is synced. It will also break public-facing links for the affected methods, but will allow us to properly link methods which currently get their anchor ids replaced.

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Here's a diff from these changes compared to the base commit:
rst-changes.zip

[akien-mga]

Adding private for methods starting with _ seems a bit weird to me, as most of those aren't private but virtual.

How about not removing leading underscores for the HTML-ification? So we'd get:

https://docs.godotengine.org/en/stable/classes/class_object.html#class-object-method-_get
https://docs.godotengine.org/en/stable/classes/class_object.html#class-object-method-get
https://docs.godotengine.org/en/stable/classes/class_object.html#class-object-method-_property-get-revert
https://docs.godotengine.org/en/stable/classes/class_object.html#class-object-method-property-get-revert

[YuriSizov]

those aren't private but virtual.

Technically they are both, which is why I went for private as a more all-encompassing option. You are not expected to call them from the outside (at least in userland).

How about not removing leading underscores for the HTML-ification?

This happens somewhere in Sphinx, I don't think we have much control over it.

[akien-mga]

Thanks!