KTOR-7596 Make multipart Content-Type check case-insensitive

[osipxd]

Subsystem
Server, ktor-http-cio

Motivation
KTOR-7596 receiveMultipart fails with "IOException: Failed to parse multipart" when content-type is capitalized

Solution
Use case-insensitive check for multipart content-type

[e5l]

lgtm

[e5l]

I would extract constant here

[osipxd]

I could add a constant ContentType.Application.TYPE. I also thought about adding an operator function contains:

public object ContentType {
    public object Application {
        public const val TYPE: String = "application"
        // ...

        public operator fun contains(contentType: CharSequence): Boolean =
            contentType.startsWith("$TYPE/", ignoreCase = true)
    }
}

And then check the content type using in:

if (contentType in ContentType.Application) { ... }

What do you think?

[osipxd]

I'll make it in a separate PR (if needed)

[e5l]

@bjhham, what do you think?

[osipxd]

I've already done some experiments locally, so here you can find a draft PR: #4433
Let's discuss there