Do not set to ref for explicit conversion and add assertion for array

type conversion. Also, add some test cases for #4901 and #4948.

test/libsolidity/syntaxTests/conversion/allowed_conversion_to_bytes_array.sol

@@ -0,0 +1,9 @@
+contract C {
+	bytes a;
+	bytes b;
+	function f() public view {
+		bytes storage c = a;
+		bytes memory d = b;
+		d = bytes(c);
+	}
+}

test/libsolidity/syntaxTests/conversion/allowed_conversion_to_string.sol

@@ -0,0 +1,9 @@
+contract C {
+	string a;
+	string b;
+	function f() public view {
+		string storage c = a;
+		string memory d = b;
+		d = string(c);
+	}
+}

test/libsolidity/syntaxTests/conversion/explicit_conversion_from_storage_array_ref.sol

@@ -0,0 +1,10 @@
+contract C {
+	int[10] x;
+	function f() public view {
+		int[](x);
+		int(x);
+	}
+}
+// ----
+// TypeError: (55-63): Explicit type conversion not allowed from "int256[10] storage ref" to "int256[] storage pointer".
+// TypeError: (67-73): Explicit type conversion not allowed from "int256[10] storage ref" to "int256".

test/libsolidity/syntaxTests/conversion/implicit_conversion_from_storage_array_ref.sol

@@ -0,0 +1,7 @@
+contract C {
+	int[10] x;
+	int[] y;
+	function f() public {
+		y = x;
+	}
+}

test/libsolidity/syntaxTests/conversion/not_allowed_conversion_to_int_array_pointer1.sol

@@ -0,0 +1,10 @@
+contract C {
+	uint[] a;
+	uint[] b;
+	function f() public view {
+		uint[] storage c = a;
+		uint[] storage d = b;
+		d = uint[](c);
+	}
+}
+// ----

test/libsolidity/syntaxTests/conversion/not_allowed_conversion_to_int_array_pointer2.sol

@@ -0,0 +1,10 @@
+contract C {
+	uint[] a;
+	uint[] b;
+	function f() public view {
+		uint[] storage c = a;
+		uint[] memory d = b;
+		d = uint[](c);
+	}
+}
+// ----