Added functionality to more easily extract plain text

[TheOriginalBytePlayer]

This pull request introduces several improvements to the PDF document API, focusing on enhancing the usability and functionality of the TPdfDocument class and exposing additional PDFium text extraction capabilities. The most important changes include updating the way PDF documents are loaded, adding indexed page access, and exposing a new function for retrieving character bounding boxes.

Enhancements to PDF document loading and access:

• Changed TPdfDocument.LoadFromFile from a procedure to a function that returns a boolean indicating success, and updated its implementation to set the result based on loading status and page count. [1] [2] [3]
• Added an indexed Pages property to TPdfDocument for direct access to pages by index.

PDFium API exposure:

• Added a new external procedure FPDFText_GetCharBox to expose PDFium's character bounding box retrieval functionality.

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[omonien]

Hi @TheOriginalBytePlayer, thanks for your interest in the project and for taking the time to submit this PR!

After careful review, I've decided not to merge this in its current form for the following reasons:

1. FPDFText_GetText is already in master - this declaration would be a duplicate.
2. 2. Breaking API change: Changing LoadFromFile from procedure to function: Boolean breaks all existing callers. The current exception-based error handling via EPdfLoadException is the intended pattern and provides richer error information than a boolean return value.
3. 3. Pages[] indexed property: Returning a TPdfPage that the caller must free from an indexed property is a memory-leak risk - users typically don't expect ownership transfer from property getters. I do like the idea though and will implement a cached version where the document manages the page lifecycle internally.
4. 4. .gitignore: The /lib entry was added twice.
      I'll be incorporating a properly designed Pages[] accessor with internal caching in an upcoming commit. Thanks again for your contribution!