Fix #4716: Crash when array index value is too large

test/libsolidity/syntaxTests/types/array_index_too_large.sol

@@ -0,0 +1,8 @@
+contract C {
+    function f() public returns (string memory) {
+        // this used to cause an internal error
+        return (["zeppelin"][123456789012345678901234567890123456789012345678901234567890123456789012345678]);
+    }
+}
+// ----
+// TypeError: (140-218): Type int_const 1234...(70 digits omitted)...5678 is not implicitly convertible to expected type uint256.