feat(chunk): split tables on even row boundaries (#3504)

**Summary**
Use more sophisticated algorithm for splitting oversized `Table`
elements into `TableChunk` elements during chunking to ensure element
text and HTML are "synchronized" and HTML is always parseable.

**Additional Context**
Table splitting now has the following characteristics:
- `TableChunk.metadata.text_as_html` is always a parseable HTML
`<table>` subtree.
- `TableChunk.text` is always the text in the HTML version of the table
fragment in `.metadata.text_as_html`. Text and HTML are "synchronized".
- The table is divided at a whole-row boundary whenever possible.
- A row is broken at an even-cell boundary when a single row is larger
than the chunking window.
- A cell is broken at an even-word boundary when a single cell is larger
than the chunking window.
- `.text_as_html` is "minified", removing all extraneous whitespace and
unneeded elements or attributes. This maximizes the semantic "density"
of each chunk.

Author: scanny

Diff for: CHANGELOG.md

@@ -1,4 +1,4 @@
-## 0.15.6-dev0
+## 0.15.6-dev1
 
 ### Enhancements
 
@@ -7,6 +7,7 @@
 ### Fixes
 
 * **Update CI for `ingest-test-fixture-update-pr` to resolve NLTK model download errors.**
+* **Synchronized text and html on `TableChunk` splits.** When a `Table` element is divided during chunking to fit the chunking window, `TableChunk.text` corresponds exactly with the table text in `TableChunk.metadata.text_as_html`, `.text_as_html` is always parseable HTML, and the table is split on even row boundaries whenever possible.
 
 
 ## 0.15.5