feat(core): add contenteditable support

[nsbarsukov]

import {Maskito, MaskitoElement, maskitoAdaptContentEditable} from '@maskito/core';

const element: MaskitoElement = maskitoAdaptContentEditable(
    document.querySelector('[contenteditable]'),
);

const maskedInput = new Maskito(element, options);

Closes #958

[github-actions]

Visit the preview URL for this PR (updated for commit ed8939c):

https://maskito--pr1039-content-editable-h204tlk8.web.app

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[nsbarsukov]

Relates to:

• feat(core): support contenteditable inputs #959
• 🚀 - Support for contenteditable inputs #958

[nsbarsukov]

@vladimirpotekhin @splincode
Guys, we have two possible solution how to add support for contenteditable:

• feat(core): add contenteditable support #1039 (by @nsbarsukov)
• feat(core): support contenteditable inputs #959 (by @aktanoff )

Both PR has many common lines but they propose different approaches.
Let's discuss and choose the final one.

[github-actions]

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