When there is an array of strutured buffers, desc sroa will only split
the array, but not a struct type in the structured buffer. However,
the calcualtion of the number of binding a struct requires does not take
this into consideration. This commit will fix that.
* Support load and extract pattern in desc_sroa.
* Fix typo in comments.
* Load replacement var before use; and added test.
* fix formatting
* Address code review comments.
