Implement caret style cursors

[NNBnh]

Split out of #1179 here is the summary:

I have always looking for a modal terminal editor that use caret style cursors,
Helix currently has implement Gap indexing #376 which mean the caret cursor dream is not far from becoming the reality.

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I thinks the movement will stay pretty much the same except for moving to the end of an object:

Because the implement Gap indexing, moving to the end of an object (e.g: a word) will place the cursor to the right of the last character of the object.

Here are some more explanation from Pepper editor:

Caret style cursors (like most text editors, cursors can move past last line character and text is always inserted to its left)

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Pepper is heavily inspired by Kakoune's selection based workflow and multiple cursors.
However its cursors behave like caret ranges instead of block selections.
That is, the cursor is not a one-char selection but only a visual cue to indicate the caret location.

Please consider implementing this feature, this will definitely make the keyboard experience way smother.

[pickfire]

I personally think it should be considered as opt-out via config, I tried vis which have this feature and I find it quite uncomformable.