Remove overlapping exclusive accesses in encoders

[itaiferber]

What's in this pull request?
{JSON,Plist}{Encoder,Decoder} had overlapping accesses which were supposed to be mutually exclusive in their with(pushedKey:) methods.

Removes those methods and the overlapping accesses.

[itaiferber]

@swift-ci Please test macOS

[itaiferber]

@swift-ci Please smoke test Linux

[norio-nomura]

It looks DecodingError.valueNotFound has duplicated _JSONKey(index: self.currentIndex) in codingPath.
Reproducing code:

import Foundation

struct A: Encodable {
    var field1: String?

    public func encode(to encoder: Encoder) throws {
        var container = encoder.unkeyedContainer()
        try container.encode(field1)
    }
}

struct B: Decodable {
    var field1: Int = 0

    public init(from decoder: Decoder) throws {
        var container = try decoder.unkeyedContainer()
        field1 = try container.decode(Int.self)
    }
}

do {
    let b = try JSONDecoder().decode(B.self, from: JSONEncoder().encode(A()))
    print(b)
} catch {
    print(error)
}

valueNotFound(Swift.Int, Swift.DecodingError.Context(codingPath: [Foundation.(_JSONKey in _12768CA107A31EF2DCE034FD75B541C9)(stringValue: "Index 0", intValue: Optional(0)), Foundation.(_JSONKey in _12768CA107A31EF2DCE034FD75B541C9)(stringValue: "Index 0", intValue: Optional(0))], debugDescription: "Expected Int but found null instead.", underlyingError: nil))

[itaiferber]

@norio-nomura Thanks for letting me know! I'll look into it

[itaiferber]

@norio-nomura What compiler version/Xcode version are you using? I see a different error on my end.

[itaiferber]

Sorry, nevermind — I was on the wrong Swift version myself. I get the same result as you do. I'll have to hunt down where we append the key to the coding path twice

[norio-nomura]

The key is appended at the line that I commented on.
Same codes exist on each decode(_:) methods of _JSONUnkeyedDecodingContainer and _PlistUnkeyedDecodingContainer.

[jrose-apple]

If you wanted to keep this with thing you could have the callback take an inout Encoder and then use $0 inside. But this works too.