6120: Pasting table into table - base scenarios.

[jodator]

Suggested merge commit message (convention)

Feature (table): Introduce pasting tables into a selected table fragment. Closes #6120.

MINOR BREAKING CHANGE: The cropTable() utility method was removed. Use cropTableToDimensions() instead.

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Additional information

This PR introduces a subset of pasting scenarios limited to:

1. The pasted table can have the same or bigger dimensions (width and/or height) than the selected table fragment. If height or width is smaller the paste is blocked (debug message is logged in the console).
2. The pasted table must be rectangular (not blocked - it will "blow" a table after paste).
3. The table selection must be rectangular (paste will be blocked with a debug message).

Other than the above scenarios that were targeted includes:

• Pasting simple (no spans) or complex (various span) table over a simple or complex fragment.
• Multiple block content inside pasted table cell contents.
• Pasting table cells with properties (borders, width, background, etc).

Additionally, I had to:

• again use Element._clone() - this will be reported somewhere
• extract some utility methods from MergeCellsCommand - again followup for cleaning the utils mess will be reported
• rewrite table cropping util to support new and old scenarios

What to not review:

• tests for cut/copy - test were extracted as paste scenarios grew
• beforementioned utility methods that were moved from command to other locations

[jodator]

Thanks for 3633a36 I've missed that locally :(