Move to #filePath when possible

[ktoso]

// SE-0274 renames #file to #filePath so that #file may refer to the name of a file instead of
// its path. From Swift 5.3+ XCTAssert* accepts #filePath and warns when a #file is passed to it.
// These functions are used to work around that.
//
// https://github.com/apple/swift-evolution/blob/master/proposals/0274-magic-file.md

There's also a workaround like this possible: https://github.com/grpc/grpc-swift/blob/1b18470db1561ef11969780c6828762565c10a10/Tests/GRPCTests/MagicFile.swift