Better error reporting

[mildm8nnered]

Implements errorDescription "correctly" (it should return String? rather than String).

Errors should now be reported correctly, rather than printing the generic "the operation could not be completed" message.

Partly addresses #6052

[SwiftLintBot]

	18 Messages
📖	Building this branch resulted in a binary size of 25052.26 KiB vs 25052.41 KiB when built on main (-1% smaller).
📖	Linting Aerial with this PR took 1.65 s vs 1.03 s on main (60% slower).
📖	Linting Alamofire with this PR took 1.38 s vs 1.39 s on main (0% faster).
📖	Linting Brave with this PR took 9.44 s vs 9.43 s on main (0% slower).
📖	Linting DuckDuckGo with this PR took 23.13 s vs 23.18 s on main (0% faster).
📖	Linting Firefox with this PR took 11.12 s vs 11.11 s on main (0% slower).
📖	Linting Kickstarter with this PR took 10.66 s vs 10.66 s on main (0% slower).
📖	Linting Moya with this PR took 0.55 s vs 0.56 s on main (1% faster).
📖	Linting NetNewsWire with this PR took 3.19 s vs 3.19 s on main (0% slower).
📖	Linting Nimble with this PR took 0.82 s vs 0.82 s on main (0% slower).
📖	Linting PocketCasts with this PR took 8.71 s vs 8.8 s on main (1% faster).
📖	Linting Quick with this PR took 0.47 s vs 0.47 s on main (0% slower).
📖	Linting Realm with this PR took 4.81 s vs 4.81 s on main (0% slower).
📖	Linting Sourcery with this PR took 2.44 s vs 2.43 s on main (0% slower).
📖	Linting Swift with this PR took 5.59 s vs 5.6 s on main (0% faster).
📖	Linting VLC with this PR took 1.45 s vs 1.45 s on main (0% slower).
📖	Linting Wire with this PR took 20.95 s vs 20.92 s on main (0% slower).
📖	Linting WordPress with this PR took 12.45 s vs 12.41 s on main (0% slower).

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