Add a theme constant to change LineEdit and TextEdit's caret width

[Calinou]

This can be useful to improve caret visibility, especially at larger font sizes. This can also be used for accessibility purposes.

This closes godotengine/godot-proposals#1220.

Preview

[YuriSizov]

Shouldn't we always multiply it by scale? And thus the default would be 1.

[Paulb23]

This doesn't seem to close godotengine/godot-proposals#1220?

Not sure about exposing the width, but rather we should port the TextEdit::CaretType over add more options.

[Calinou]

This doesn't seem to close godotengine/godot-proposals#1220?

This PR provides a close enough solution for the 90% use case. Using arbitrary textures for the caret is a very uncommon use case, and I don't feel it's worth supporting in core. As long as there's a way to get the caret position in pixels, it's possible to hide the default caret by setting its color to Color(0, 0, 0, 0) and draw a textured caret manually.

[bruvzg]

Shouldn't we always multiply it by scale? And thus the default would be 1.

I agree, it's probably better to always use theme scaling, otherwise looks good.

[Calinou]

Rebased and tested again, it works as expected.

[YuriSizov]

Shouldn't we always multiply it by scale? And thus the default would be 1.

Will you address this concern? 🙃

[Calinou]

Will you address this concern? 🙃

Done (and tested again) 🙂

I thought I had addressed it before, but I didn't.

[akien-mga]

Thanks!