Problems with the interface file

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I discovered two problems related to the "Add to interface file" feature.

1. If the identifier name is an operator, the generated code in the interface file will be malformed (missing parentheses), causing a syntax error. For instance:

let (/==) = (a: int, b: int): int => a + b;

results in

let /==: (int, int) => int;

2. "Add to interface file" doesn't appear for explicit modules. That is, it's not possible to generate a corresponding module type in the interface file with the feature.

Start by locating the implementation of the "Add to interface file" feature and reproduce the operator example to inspect the malformed generated code. Then investigate the explicit-module path; done means operator identifiers generate valid interface syntax and explicit modules offer corresponding module types.

Written by the indexing model from the issue text.