Update FPDFFont_* bindings and implementations

[ajrcarey]

Follow-on from #137, #151. Upgrading to Pdfium release 6611 from https://github.com/bblanchon/pdfium-binaries/releases/download/chromium%2F6611/pdfium-linux-x64.tgz results in failed static builds because the FPDFFont_GetFontName() function has been removed, replaced instead with separate FPDFFont_GetBaseFontName() and FPDFFont_GetFamilyName() functions.

Additionally, new FPDFFont_GetFontData() and FPDFFont_GetIsEmbeded() functions have been added.

Update all bindings and implementations to match.

[ajrcarey]

FPDFFont_GetBaseFontName() is in the Pdfium source export headers, but has not yet been published at https://github.com/bblanchon/pdfium-binaries yet.

[ajrcarey]

Used version feature flags introduced in #153 to appropriately version FPDFFont_GetFontName() (pre-6611), FPDFFont_GetBaseFontName() (post-6611), and two separate versions of FPDFFont_GetFamilyName() (the pointer argument and return types differ between Pdfium release 6611 and the Pdfium source mainline head that will form the next release).

Awaiting next Pdfium release to update version flags and close out. Should be possible to include in 0.8.25.

[ajrcarey]

Added backward compatibility checks to .github/workflows/build_test.yml to detect bindings breakage across Pdfium API versions. Removed some unnecessary feature gates from bindings.rs. Merged in related pull request #155.

[ajrcarey]

Pdfium release 6666 includes all changes. Updated bindings for pdfium_6666 and pdfium_future features. Removed TODOs. All workflow checks passed.

[ajrcarey]

Waiting on completion of #137. Will be released in crate version 0.8.25.