Move range_tree, btree, highbit64 to common code

Break out the range_tree, btree, and highbit64/lowbit64 code from kernel
space into shared kernel and userspace code.  This is needed for the
updated `zpool status -vv` error byte range reporting that will be
coming in a future commit.  That commit needs the range_tree code in
kernel and userspace.

Reviewed-by: Rob Norris <robn@despairlabs.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Closes #18133

cmd/zpool/zpool_util.h

@@ -45,8 +45,6 @@ void *safe_realloc(void *, size_t);
 void zpool_no_memory(void);
 uint_t num_logs(nvlist_t *nv);
 uint64_t array64_max(uint64_t array[], unsigned int len);
-int highbit64(uint64_t i);
-int lowbit64(uint64_t i);
 
 /*
  * Misc utility functions