build: add tesseract library linking for hardsubx feature

[DhanushVarma-2]

Fixes #1719

Problem: The build fails when using --enable-hardsubx and --enable-ocr flags due to missing tesseract library linking, even though hardsubx uses tesseract OCR functions.

Solution: Added pkg_check_modules for tesseract and leptonica in the HARDSUBX section of src/CMakeLists.txt, similar to how OCR section handles these libraries.

Changes:

• Added tesseract and leptonica library detection in HARDSUBX CMake section
• Added library linking for both tesseract and leptonica
• Added include directories for both libraries

Testing: Tested build with: bash cmake -DWITH_HARDSUBX=ON -DWITH_OCR=ON -DWITH_FFMPEG=ON make