cover results of LAYOUT features

[bertsky]

So far, we only convert the basic page layout and TABLE feature results, but if the AWS query contains LAYOUT in FeatureTypes, then we do get rich layout hierarchy (last paragraph of Block types in Textract Layout API Reference:

• LAYOUT_TITLE - The main title of the document.
  → TextRegion with @type=heading
• LAYOUT_HEADER - Text located in the top margin of the document.
  → TextRegion with @type=header
• LAYOUT_FOOTER - Text located in the bottom margin of the document.
  → TextRegion with @type=footer
• LAYOUT_SECTION_HEADER - The titles of sections within a document.
  → TextRegion with @type=heading, too
• LAYOUT_PAGE_NUMBER - The page number of the documents.
  → TextRegion with @type=page-number
• LAYOUT_LIST - Any information grouped together in list form.
  → TextRegion with @type=other,
  • but perhaps we could also set @type=list in the ReadingOrder/OrderedGroup
• LAYOUT_FIGURE - Indicates the location of an image in a document.
  → ImageRegion
• LAYOUT_TABLE - Indicates the location of a table in the document.
  → TableRegion
  • (but how does that interfere with blocks of TABLE type??)
• LAYOUT_KEY_VALUE - Indicates the location of form key-values in a document.
  → unclear, probably connected to KEY_VALUE_SET blocks
• LAYOUT_TEXT - Text that is present typically as a part of paragraphs in documents.
  → TextRegion with @type=paragraph