Added possibility to set additional directories to search fonts

[adelobosko]

• fixed typo in WindowsSystemFontLister (PSFonts dir was not included, fonts dir was used twice instead)

• added possibility to set additional directories to search fonts

useful for strict environments without preinstalled fonts or without access to them
related to BobLd/PdfPig.Rendering.Skia#145

[BobLd]

@adelobosko thanks a lot for the PR, I think this is going to help many users.

I have added comments - let me know if any questions

The feedback in AndroidSystemFontLister.cs is applicable to all other ISystemFontLister implementations

[BobLd]

@adelobosko I did a 2nd pass on the code, have you successfully added other fonts in your use case?

AdditionalFontSearchDirectories is used inside Lazy<>, so once the lazy value is actually created, adding new font path won't do anything, and this happens silently.

We should aim at throw an exception if a path is added too late.

[adelobosko]

@BobLd Yes, I was able to successfully add other fonts in my use case.

[BobLd]

@adelobosko thanks for updating the PR.

Regarding my last comment, your FontSearchDirectoryLock does not do anything for the moment (and it's gating a concurrent bag).

Can you review your changes?

As a side note: I agree with the approach being static (even if not a huge fan, but I don't think there's an alternative), it just need to be robust.

[adelobosko]

Regarding my last comment, your FontSearchDirectoryLock does not do anything for the moment (and it's gating a concurrent bag).

FontSearchDirectoryLock preventing duplicates, maybe better to use HashSet + lock instead of Concurrent bag

[BobLd]

@adelobosko agreed on the hashset, yes. My comment above was related to the use of AvailableFonts.IsValueCreated. It is not enough as a gate, FontSearchDirectoryLock should also be lock inside the lazy creation method.

Will merge as-is and push changes for the lock, and hashset.

[adelobosko]

@BobLd done, changed to HashSet + locks

[BobLd]

@adelobosko thx for the updates. Can you let me know when you are done? I'll run the tests and merge

[adelobosko]

@BobLd It's done