Spellcheck and cursor improvements

[streamich]

• Disable spellcheck in inline elements spellCheck={false}, which are split by cursor.
  • Improve inline block React node generation code. Modify props of previous not to specify it might have a cursor.
    • Improve positioning approach of caret, when it is attached to "after" the character. Instead of absolute position shift, figure out the positioning logic inside the new inline element rendering loop.
• Or, render cursor as a virtual overlay.