Add a prop to RichText native to allow configuration of selection/caret color

[SergioEstevao]

Description

Allow the passing of the selectionColor downstream to the native rich text component.

How has this been tested?

This can be tested using this PR in GB-mobile: wordpress-mobile/gutenberg-mobile#1776

Screenshots

Types of changes

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR. .

[mtias]

Is this meant to be a public API for rich-text?

[chipsnyder]

@mtias Yup there was an open request to expose a mechanism to support changing the highlight and caret color in mobile to make it easier to see in dark mode. You can find the original issue here with some helpful screenshots wordpress-mobile/gutenberg-mobile#1773

Edited wording

[mtias]

But wouldn't that be handled by a theme context rather than direct prop setting — which I don't expect block authors to do —?

[lukewalczak]

this.props.selectionColor is an additional, not required prop (if not passed selectionColor is specified by a system). In most cases, it should have the same color as text within RichText, so imo it doesn't have to be handled by a theme context.

[lukewalczak]

I don't have a strong opinion about it, but since on web caret color is the same as text color, maybe selectionColor should be

selectionColor={ this.props.selectionColor || (style && style.color) }

[SergioEstevao]

But wouldn't that be handled by a theme context rather than direct prop setting — which I don't expect block authors to do —?

@mtias At the moment because we still don't a have a proper way to style the components in mobile using themes (css on the web) we have a lot of properties like this that are set directly in the blocks: textColor, placeholderColor, etc.
So this selectionColor prop is just like the above, and probably in the future can be remove from the wordpress RichText component and we can use a style/theme to set it.

[SergioEstevao]

I don't have a strong opinion about it, but since on web caret color is the same as text color, maybe selectionColor should be
selectionColor={ this.props.selectionColor || (style && style.color) }

If we do this change we will change the selectionColor on all the blocks we already have implemented to be black/gray instead of the current default light blue. I don't think this is something we want.

[pinarol]

LGTM!