Support most cases of sizeof applied to an expression

Previously there was only support for `sizeof(<type>)` and expressions
which syntactically look like a type (such as `sizeof(foo)`).

Fixes #2091.

Examples/test-suite/constant_expr_c.i

@@ -32,4 +32,25 @@ double d_array[12 % 9];
 #define TEST_I 0
 #endif
 
+/* sizeof didn't work on an expression before SWIG 4.1.0 except for cases where
+ * the expression was in parentheses and looked syntactically like a type (so
+ * sizeof(X) worked because X could be a type syntactically).
+ */
+const int s1a = sizeof(X); /* worked before 4.1.0 */
+//const int s1b = sizeof X; /* not currently supported */
+const int s2a = sizeof("a string" );
+const int s2b = sizeof "a string";
+const int s3a = sizeof('c');
+const int s3b = sizeof('c');
+const int s4a = sizeof(L"a wstring");
+const int s4b = sizeof L"a wstring";
+const int s5a = sizeof(L'C');
+const int s5b = sizeof L'C';
+const int s6a = sizeof(sizeof(X));
+const int s6b = sizeof sizeof(X);
+const int s7a = sizeof(3.14);
+const int s7b = sizeof 3.14;
+const int s8a = sizeof(2.1e-6);
+const int s8b = sizeof 2.1e-6;
+
 %}