Type fixes

These were mostly found by trying compiling the source as C++ instead of C, which enforces more strict type checking.

The only notable pattern of errors here: While the enumerants are of VkAsdfFlagBits type, they are actually passed/assigned to variables of VkAsdfFlags (and similarly for XR). I suspect this is to avoid the issues with bitwise-or of two enumerants not returning a value of the same enumerant type - all those VkAsdfFlags types are essentially just uint64_t.