KTOR-7190: Add support for encoded non-text queries

[demitsuri]

Subsystem
The changes only affect URLBuilder internals and some other internal APIs. No public API was affected.

Motivation
It fixes https://youtrack.jetbrains.com/issue/KTOR-7190/URLBuilder.encodedParameters-cant-handle-encoded-non-text-query-data.

Solution
Former solution assumed that any query parameter is able to be decoded as an UTF-8 string. And any encoded query parameter was decoded during the building an URL and after that encoded back to create a textual representation of an URL. Unfortunately it crashes an app if it tries to add something like bittorrent info_hash parameter (also see #1351 (comment)) because there are a lot of byte sequences which can't be decoded as an UTF-8 string.

My solution reverses the data flow. I added one special ParametersBuilder for undecodable query parameters where they are stored in encoded form. And URLBuilder.encodedParameters became just a wrapper which stores decodable parameters in URLBuilder.parameters and undecodable ones in the private URLBuilder.rawEncodedParameters.

[demitsuri]

@bjhham Please take a look.

[bjhham]

So there's a few things I don't like about this approach of using two maps for the parameters:

1. The order of the parameters coming out is not the same as it is going in.
2. It further complicates an already-complicated set of types.
3. It creates problems for any code interacting with Url.parameters where it's expecting a complete set.

I'd propose removing the isDecodable function and instead introducing a new line of functions like String.tryDecode that instead returned a sealed type UrlString { Decoded, Encoded }, then the Parameters and ParametersBuilder types can just use these types internally instead of decoding everything then encoding again later.

I can help with updating the Parameter types if you'd like; I've been working on a pretty large refactor of our URL types to try to resolve some of our problems with default requests etc.

[demitsuri]

@bjhham Thank you for your review. I'll try to update the code according to your proposal shortly.