refactor(ios): Rename FileUtils to FilePickerUtils

[vicajilau]

Renames the FileUtils class and source files to FilePickerUtils in the iOS implementation. This includes updating the class definition, implementation, and the umbrella header import.

Fixed: #1921

[navaronbracke]

@vicajilau I think we should evaluate if we can rewrite the plugin in Swift (using the shared darwin source option)

That would make contributing a lot easier, too.

[vicajilau]

@navaronbracke From what I can see, sharedDarwinSource only serves to unify flows on iOS and macOS. But I wouldn't mind rewriting the Objective-C code in Swift. Shall we create an issue to follow up on this?

[navaronbracke]

@navaronbracke From what I can see, sharedDarwinSource only serves to unify flows on iOS and macOS. But I wouldn't mind rewriting the Objective-C code in Swift. Shall we create an issue to follow up on this?

Correct. My suggestion is that we rewrite the MacOS portion in Swift, and unify with iOS in the same refactor.
We can follow up with a new feature request issue.

Maybe we can do that in two passes though (one Obj-C -> Swift for MacOS PR, one sharedDarwinSource:true PR)