fix(407): clear text on action menu click

[Nikolai-featurebase]

Description

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

Fixes #407

Type of change

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• I have performed a self-review of my own code
• I have commented on my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have checked my code and corrected any misspellings

[Darginec05]

It can break logic for complex blocks with multiple nested Slate children.
My suggesstion:

    const lastNode = Editor.last(newSlate, [0]);
    Transforms.delete(newSlate, { at: lastNode[1] });