LibCrypto: Add a way to compare a SignedBigInteger with a double

This supports any double value (except for NaNs) instead of having to
cast the double to some smaller type which doesn't work for very large
values.

Userland/Libraries/LibCrypto/BigInt/SignedBigInteger.h

@@ -139,6 +139,14 @@ public:
     [[nodiscard]] bool operator<(UnsignedBigInteger const& other) const;
     [[nodiscard]] bool operator>(UnsignedBigInteger const& other) const;
 
+    enum class CompareResult {
+        DoubleEqualsBigInt,
+        DoubleLessThanBigInt,
+        DoubleGreaterThanBigInt
+    };
+
+    [[nodiscard]] CompareResult compare_to_double(double) const;
+
 private:
     void ensure_sign_is_valid()
     {