* BorrowedAccount: add set_data_from_slice(), make set_data() take owned values
set_data() used to take a slice and would force alloc+copy if the caller
has owned values (eg account creation, account lookup table).
Expose set_data_from_slice() for callers that have slices, and switch
set_data() to taking an owned Vec.
* BorrowAccount: refactor common accounts_update_delta code in helper method
* BorrowedAccount: add extend_from_slice()
This allows avoiding copies appending entries to account lookup tables.
* BorrowedAccount: remove unnecessary ifs around update_accounts_resize_delta
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