pidl: add support for [string] on fixed size arrays.

pidl: add support for [string] on fixed size arrays.

midl also supports this:

struct {
	long l1;
	[string] wchar_t str[16];
	long l2;
};

Where the wire size of str is encoded like a length_is() header:
4-byte offset == 0;
4-byte array length;

The strings are zero terminated.

metze
(cherry picked from commit 7ccc9a6ef563cc855752b4e74152420b9be5af43)