Add option to remove underline in Editor Docs

[Mickeon]

The current Docs are certainly an improvement in style, but there's something that has always given me enough of a headache to instead look up the Docs online, and I can't help but feel like the problem I personally have is much more pronounced for users that have trouble reading in general (poor vision, dyslexia...).

This PR adds a new Editor Setting "text_editor/help/show_meta_underline". This is enabled by default.

On	Off

When disabled, it can definitely be said that the text becomes much cleaner to read. To further sell the deal, in this PR, meta words change cursor shape on hover, regardless of setting:

(In the future, this may actually be useful to show meaningful tooltips in the Editor Documentation, too)

[Calinou]

Could we improve the underline styling to make it less of a problem with regards to readability (e.g. by increasing the spacing or reducing its opacity)? I'd prefer doing this over adding an editor setting (so the solution benefits everyone automatically).

[Mickeon]

The underline is hardcoded to be drawn with draw_line() to be the same colour as the font. It would be possible to make the colour more transparent, but that is not always the desired result. The spacing as is currently is suitable, actually. The problem is the density of the underlines. Increasing the spacing downwards may only make the issue worse.

An addition to this that may suit everyone, however, is having the underline display only when hovered on. It may(?) be possible to do this without touching the Rich Text Label code. This is pretty much standard behaviour across browsers and applications, already, too.

[Calinou]

An addition to this that may suit everyone, however, is having the underline display only when hovered on.

I don't like when websites do this – it makes it hard to know what's a link and what's not without having to point at everything with the mouse. I much prefer having a visible underline at all times, even if it's faint.

[Mickeon]

Unfortunately that sounds very much like a preference matter. Therefore it can still be argued whether or not this "underline" thing should still be an Editor Setting, or not.

[akien-mga]

We discussed this in a PR meeting. This calls for digging a bit further to find the One True Style to rule them all. We should aim to harmonize the display in the editor help and in the online docs. Some examples of differences which impact this change:

• All types are listed in blue in the editor help's table, but some of them (void) are not clickable. If we remove the underlines, we don't know which types are clickable unless they're hovered. The online docs don't have this problem as all links are blue, and non-links are black.
• Similarly, the inline hyperlinks have a background box which is the same as non-clickable inline code. Removing the underline also makes it harder to know which "inline code" markup is a link or not.

[YuriSizov]

• All types are listed in blue in the editor help's table, but some of them (void) are not clickable. If we remove the underlines, we don't know which types are clickable unless they're hovered. The online docs don't have this problem as all links are blue, and non-links are black.

Seems like this has been (partially?) addressed by #68159.

Similarly, the inline hyperlinks have a background box which is the same as non-clickable inline code. Removing the underline also makes it harder to know which "inline code" markup is a link or not.

And this was changed in #68132.

[Mickeon]

I want to note one complication of adding underlines on hover would be requiring custom logic for it, because RichTextLabel does not support it, kind of similarly to what the Script Editor does when holding CTRL.

[akien-mga]

Superseded by #89049.

[Mickeon]

Oh noes what a shame!