Adding event and error selector fields on the lines of the function selector fields

test/libsolidity/syntaxTests/errors/error_selector_syntax.sol

@@ -0,0 +1,48 @@
+library L {
+    error E();
+}
+library S {
+    error E(uint);
+}
+library T {
+    error E();
+}
+
+error E();
+
+interface I {
+    error E();
+    function f() external pure;
+}
+
+contract D {
+    error F();
+}
+
+contract C is D {
+    function test1() public pure returns (bytes4, bytes4, bytes4, bytes4) {
+        assert(L.E.selector == T.E.selector);
+        assert(L.E.selector != S.E.selector);
+        assert(E.selector == L.E.selector);
+        assert(I.E.selector == L.E.selector);
+        return (L.E.selector, S.E.selector, E.selector, I.E.selector);
+    }
+
+    bytes4 s1 = L.E.selector;
+    bytes4 s2 = S.E.selector;
+    bytes4 s3 = T.E.selector;
+    bytes4 s4 = I.E.selector;
+
+    function test2() view external returns (bytes4, bytes4, bytes4, bytes4) {
+        return (s1, s2, s3, s4);
+    }
+
+    function test3() pure external returns (bytes4) {
+        return (F.selector);
+    }
+}
+// ----
+// Warning 2519: (16-26): This declaration shadows an existing declaration.
+// Warning 2519: (45-59): This declaration shadows an existing declaration.
+// Warning 2519: (78-88): This declaration shadows an existing declaration.
+// Warning 2519: (122-132): This declaration shadows an existing declaration.