Add native pdfium text extract/search support in Pdfiumcore

[simonbellu]

Why not adding native pdfium text extract /search support for using with AndroidPdfViewer Beta 3.2.0? Please do it. Thank you.

[odmfl]

pdfium should have this function, the problem is to implement it for android. I remember the old app "google pdf viewer" which however was based on pdfium and had this function

I did some research and found some libraries that have implemented the search, but I don't know if they work, they should be tested. It would take someone to test them and maybe fork and keep an updated fork.

Test them and let me know if they work in any way

https://github.com/gulshan98185/AndroidPdfViewer

https://github.com/beeline09/AdvancedPdfView

https://github.com/beeline09/android-support-pdfium

https://github.com/benjinus/android-support-pdfium