Split fallback function and introduce "fallback()" and "receive()" syntax.

test/libsolidity/syntaxTests/inheritance/fallback_receive/fallback_overrides_receive.sol

@@ -0,0 +1,8 @@
+contract C {
+	receive() external payable {}
+}
+contract D is C {
+	fallback() override external {}
+}
+// ----
+// TypeError: (76-84): Function has override specified but does not override anything.

test/libsolidity/syntaxTests/inheritance/fallback_receive/fallback_with_override.sol

@@ -0,0 +1,6 @@
+contract C {
+	fallback() external {}
+}
+contract D is C {
+	fallback() override external {}
+}

test/libsolidity/syntaxTests/inheritance/fallback_receive/fallback_with_override_intermediate.sol

@@ -0,0 +1,8 @@
+contract C {
+	fallback() external {}
+}
+contract D is C {
+}
+contract E is D {
+	fallback() override external {}
+}

test/libsolidity/syntaxTests/inheritance/fallback_receive/fallback_without_override.sol

@@ -0,0 +1,8 @@
+contract C {
+	fallback() external {}
+}
+contract D is C {
+	fallback() external {}
+}
+// ----
+// TypeError: (58-80): Overriding function is missing 'override' specifier.

test/libsolidity/syntaxTests/inheritance/fallback_receive/fallback_without_override_intermediate.sol

@@ -0,0 +1,10 @@
+contract C {
+	fallback() external {}
+}
+contract D is C {
+}
+contract E is D {
+	fallback() external {}
+}
+// ----
+// TypeError: (78-100): Overriding function is missing 'override' specifier.

test/libsolidity/syntaxTests/inheritance/fallback_receive/receive_overrides_fallback.sol

@@ -0,0 +1,8 @@
+contract C {
+	fallback() external {}
+}
+contract D is C {
+	receive() override external payable {}
+}
+// ----
+// TypeError: (68-76): Function has override specified but does not override anything.

test/libsolidity/syntaxTests/inheritance/fallback_receive/receive_with_override.sol

@@ -0,0 +1,6 @@
+contract C {
+	receive() external payable {}
+}
+contract D is C {
+	receive() override external payable {}
+}

test/libsolidity/syntaxTests/inheritance/fallback_receive/receive_with_override_intermediate.sol

@@ -0,0 +1,8 @@
+contract C {
+	receive() external payable {}
+}
+contract D is C {
+}
+contract E is D {
+	receive() override external payable {}
+}

test/libsolidity/syntaxTests/inheritance/fallback_receive/receive_without_override.sol

@@ -0,0 +1,8 @@
+contract C {
+	receive() external payable {}
+}
+contract D is C {
+	receive() external payable {}
+}
+// ----
+// TypeError: (65-94): Overriding function is missing 'override' specifier.

test/libsolidity/syntaxTests/inheritance/fallback_receive/receive_without_override_intermediate.sol

@@ -0,0 +1,10 @@
+contract C {
+	receive() external payable {}
+}
+contract D is C {
+}
+contract E is D {
+	receive() external payable {}
+}
+// ----
+// TypeError: (85-114): Overriding function is missing 'override' specifier.