Add line size metrics (ascender, descender, size) to line objects in blocks output

[Balearica]

There is currently no easy way to retrieve accurate line size metrics using Tesseract.js. Several sub-optimal ways of accomplishing this are listed below.

• Use word object within blocks output format.
  • These metrics are rarely accurate, and unhelpful without additional information
    • There is no absolute mapping between font size and pixels
• Use ascender/descender/x_size metrics in hocr output
  • These are useful and accurate (at least using Tesseract Legacy)
  • Unfortunately, getting the values is a hassle
    • Extracting requires using an XML parser or regular expressions
• Calculate font size manually using character-level bounding boxes
  • This works, but is even more of a hassle than parsing from HOCR

The ascender/descender/row_height metrics from the hocr output should be added to the blocks output format. This will allow for easily retrieving accurate data about line size.

[Balearica]

There is a RowAttributes getter in Tesseract, however it is not accessible through Tesseract.js-core because of how recently it was added. Therefore, implementing this will require a new minor version of Tesseract.js-core. The implementation should be sure not to break code for users with old versions of Tesseract.js-core.