Fix DLLs to be Tesseract 5.2

[Methuselah96]

It looks like this commit attempted to update to Tesseract 5.2, but the Tesseract DLL was not actually updated to 5.2 (and a Tesseract 5.2 EXE was added instead).

This PR:

• Updates the Tesseract DLL to 5.2 and updates the tests as a result.
• Adds a GitHub Actions CI to automatically build the Leptonica and Tesseract DLLs with an output that can be downloaded and included in a PR (as it is in this one).
• Updates the existing GitHub Actions CI to be run on all PRs and pushes to master. It has been cleaned up and only runs on Windows at the moment, but I hope to expand it to run on Linux and macOS in the future.

[Methuselah96]

The DLLs that were added were downloaded from this build. The MD5 hashes are printed as part of the build and can be verified by hashing the DLLs locally.

[AlexPieczynski]

This file actually contains an image of the letter "T". However, the margin on the right-hand side of "T" is smaller than the left, and I think that's causing the auto-thresholding algorithm to invert the thresholding and recognize the text as "hl" instead. I updated the PNG and got the expected result:
OLD:
https://github.com/charlesw/tesseract/blob/master/src/Tesseract.Tests/Data/Ocr/PSM_SingleChar.png
NEW:

[Methuselah96]

I was planning to look into that and make sure that was a regression with the Tesseract library itself, and not an issue with the C# wrapper, thanks for looking into it. I'm surprised that the Tesseract library would return more than one character when it's explicitly instructed to only return a single character.

[AlexPieczynski]

You make an interesting point about Tesseract returning 2 characters despite the PageSegMode; might be worth digging into deeper as a potential Tesseract library defect.