Typescript builds empty content arrays in paragraphs

[Craig Lawrence]

CS generates ADF paragraph nodes containing empty content arrays, so we should match that temporarily for the rollout.

e.g.

• Request |a| |b|
• CS {"type":"tableCell","attrs":{},"content":[{"type":"paragraph","content":[]}
• Lib {"type":"tableCell","attrs":{},"content":[{"type":"paragraph"}

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