Merges text files from Document AI output shards into a single text file corresponding to the parent document.
folder path for input files
folder path for output files
no return value, called for side effects
The function works on .txt files generated from .json output files,
not on .json files directly. It also presupposes that the .txt filenames
have the same name stems as the .json files from which they were extracted.
For the v1 API, this means files ending with "-0.txt", "-1.txt", "-2.txt",
and so forth. For the v1beta2 API, it means files ending with
"-page-1-to-100.txt", "-page-101-to-200.txt", etc. The safest approach is
to generate .txt files using
text_from_dai_file() with the
parameter set to TRUE.