Add support for stake::split() via create_account_with_seed()

[rob-solana]

Problem

stake::split() into an account with a _with_seed() address isn't part of
the stake_instruction API, so must be hand-rolled.

Summary of Changes

add the API to get that instruction vector
note: depends on #7776

Fixes #

[rob-solana]

split() is special, in the ideal case:

• there's no transfer, except among stake accounts
• it requires only one signature: the authorized staker (implies the fee payer is the authorized staker)

So, the split() destination account needs to:

• wink into existence (potentially with zero lamports)
• get initialized

implies support for a "create account with no transfer" message constructor (is part of #7776 )

[codecov]

Codecov Report

Merging #7785 into master will increase coverage by <.1%.
The diff coverage is 90.9%.

@@           Coverage Diff            @@
##           master   #7785     +/-   ##
========================================
+ Coverage    81.8%   81.8%   +<.1%     
========================================
  Files         238     241      +3     
  Lines       50993   51080     +87     
========================================
+ Hits        41730   41830    +100     
+ Misses       9263    9250     -13