gnucash maint: [assistant-stock-transaction] refactor: centralize price calculator

[Christopher Lam]

Updated	 via  https://github.com/Gnucash/gnucash/commit/6ba0f849 (commit)
	from  https://github.com/Gnucash/gnucash/commit/9a8bc8f7 (commit)



commit 6ba0f849ba925e797d1ab65f5374db7740139c53
Author: Christopher Lam <christopher.lck at gmail.com>
Date:   Sat Sep 17 22:51:18 2022 +0800

    [assistant-stock-transaction] refactor: centralize price calculator
    
    Price was being computed in 3 places: the stock_value page, the
    summary-table info list, and the final pricedb creation function. This
    commit centralizes it into 1 function which returns std::nullopt if
    the price is not computable.
    
    Also fixes price display to follow global pref general/force-price-decimal



Summary of changes:
 gnucash/gnome/assistant-stock-transaction.cpp | 62 +++++++++++++++------------
 1 file changed, 34 insertions(+), 28 deletions(-)