is duplicated by:

• SR-13350 @_exported import does not properly export custom operators

Issue Description:

Exporting a module using `@_exported` does not export custom operators declared in that module.

I've created a reproduction of this bug here:
https://github.com/tanner0101/swift-operator-bug

To exhibit the bug, run `swift build`.

You should see the following error when building module `C`:

/Users/tanner/dev/tanner0101/swift-operator-bug/Sources/C/main.swift:3:9: error: operator is not a known binary operator
print(1 ~~ 2)
        ^

This error can be worked around by manually importing module `A` where `~~` is defined. However, this should not be required since module `B` is imported by `C` and module `A` is `@_exported` by module `B`.

Module A:

infix operator ~~
public func ~~(lhs: Int, rhs: Int) -> Bool {
    lhs == rhs
}

Module B:

@_exported import A

Module C:

import B

print(1 ~~ 2) // Does not work