feat: Improve the LayoutPostprocessor

[nikos-livathinos]

LayoutPostprocessor improvements:

• Do not throw away Formulas which have no assigned cells (neither programmatic nor OCR)
• Add some post-processing heuristics that look at the text to descide if a cluster label must be corrected
  • (e.g. flip text to caption label when the text starts with "fig" or "table")
• Go through issues labeld with "layout", pick provided inputs, and decide if to make CVAT GT for it
• Disable orphan creation code and check if it improves mAP
• ...

Checklist:

• Documentation has been updated, if necessary.
• Examples have been added, if necessary.
• Tests have been added, if necessary.

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