Regression: `String.data(using: .iso2022JP)` unexpectedly returns `nil` on non-Darwin.

[YOCKOW]

Given the following code:

import Foundation
print("Hello, world!".data(using: .iso2022JP) as Any)

Results are:

OS	Swift	Result
macOS	5.10	"Optional(13 bytes)"
Ubuntu	5.10	"Optional(13 bytes)"
macOS	6.0	"Optional(13 bytes)"
Ubuntu	6.0	"nil"

This is regression from Swift 6 on Linux.
Note that ISO-2022-JP is often used for MIME(Email) in Japan.

Relates to: #925

[parkera]

Resolved by #1217 as long as Foundation is imported.

[YOCKOW]

Confirmed this is fixed in swift-DEVELOPMENT-SNAPSHOT-2025-05-11-a.