refactor(options): remove option type macros

Problem: We have `P_(BOOL|NUM|STRING)` macros to represent an option's type, which is redundant because `OptValType` can already do that. The current implementation of option type flags is also too limited to allow adding multitype options in the future.

Solution: Remove `P_(BOOL|NUM|STRING)` and replace it with a new `type_flags` attribute in `vimoption_T`. Also do some groundwork for adding multitype options in the future.

Side-effects: Attempting to set an invalid keycode option (e.g. `set t_foo=123`) no longer gives an error.

src/nvim/math.c

@@ -40,3 +40,29 @@ int xisnan(double d)
 {
   return FP_NAN == xfpclassify(d);
 }
+
+/// Count trailing zeroes at the end of bit field.
+int xctz(uint64_t x)
+{
+  // If x == 0, that means all bits are zeroes.
+  if (x == 0) {
+    return 8 * sizeof(x);
+  }
+
+  // Use compiler builtin if possible.
+#if defined(__clang__) || (defined(__GNUC__) && (__GNUC__ >= 4))
+  return __builtin_ctzll(x);
+#else
+  int count = 0;
+  // Set x's trailing zeroes to ones and zero the rest.
+  x = (x ^ (x - 1)) >> 1;
+
+  // Increment count until there are just zero bits remaining.
+  while (x) {
+    count++;
+    x >>= 1;
+  }
+
+  return count;
+#endif
+}