Explicitly add type annotations to exported constants in expr-library

[AnyhowStep]

Instead of,

export const concat = makeOperator1ToN<OperatorType.CONCAT, string, string>(
    OperatorType.CONCAT,
    tm.string(),
    TypeHint.STRING
);

Use this,

export const concat : Operator1ToN<string, string> = makeOperator1ToN<OperatorType.CONCAT, string, string>(
    OperatorType.CONCAT,
    tm.string(),
    TypeHint.STRING
);

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We cannot rely on type inference. We need to explicitly add type annotations or AMD declaration emit will break.

Keep an eye on this,
microsoft/TypeScript#37267