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.h

@@ -1,5 +1,14 @@
 #pragma once
 
+#include <stdbool.h>
+#include <stdint.h>
+
+/// Check if number is a power of two
+static inline bool is_power_of_two(uint64_t x)
+{
+  return x != 0 && ((x & (x - 1)) == 0);
+}
+
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "math.h.generated.h"
 #endif