Support creation of structure inside structures in types sidebar

[op2786]

Most of the time I encounter a structures that have another structure in it whose members become visible over time. In the example below, I know that at offset 0x10 of wsa_ctx there is another structure that holds data buffer which have 2 four bytes member. In this case, I want to select both data and field_14 and create a structure there by pressing S.

Currently, BN creates a stucture with no members and do not modify wsa_ctx. I expect BN creates that structure, put it in the wsa_ctx's offset 0x10 and get rid of data and field_14.