Replace "pragma experimental ABIEncoderV2" in tests where appropriate

And add a few tests for "pragma abicoder".

test/libsolidity/syntaxTests/abiEncoder/conflicting_settings_reverse.sol

@@ -1,4 +1,4 @@
 pragma abicoder v1;
-pragma experimental ABIEncoderV2;
+pragma abicoder v2;
 // ----
-// SyntaxError 8273: (20-53): ABI coder v1 has already been selected through "pragma abicoder v1".
+// SyntaxError 3845: (20-39): ABI coder has already been selected for this source unit.

test/libsolidity/syntaxTests/abiEncoder/conflicting_settings_reverse_experimental.sol

@@ -0,0 +1,4 @@
+pragma abicoder v1;
+pragma experimental ABIEncoderV2;
+// ----
+// SyntaxError 8273: (20-53): ABI coder v1 has already been selected through "pragma abicoder v1".

test/libsolidity/syntaxTests/abiEncoder/select_v1_quoted_string.sol

@@ -0,0 +1 @@
+pragma abicoder "v1";

test/libsolidity/syntaxTests/abiEncoder/select_v2_quoted_string.sol

@@ -0,0 +1 @@
+pragma abicoder "v2";