gnucash stable: Multiple changes pushed

[John Ralls]

Updated	 via  https://github.com/Gnucash/gnucash/commit/8481f062 (commit)
	 via  https://github.com/Gnucash/gnucash/commit/0d175dce (commit)
	 via  https://github.com/Gnucash/gnucash/commit/e8c80f2f (commit)
	from  https://github.com/Gnucash/gnucash/commit/9ff2362b (commit)



commit 8481f062d45d99c506f77f920e4ae1a859b19c35
Author: John Ralls <jralls at ceridwen.us>
Date:   Fri Apr 28 16:58:44 2023 -0700

    Create obsolete features list with first member book_currency.
    
    Obsolete features set in the book will be removed from the book's
    KVP and ignored. Note the warning in the comment!

commit 0d175dce12239eda4db54e3d93c3cb6ebbdfe0f9
Author: John Ralls <jralls at ceridwen.us>
Date:   Fri Apr 28 16:31:07 2023 -0700

    Refactor gnc-features.
    
    * type aliases to gnc-features.h
    * string_views to avoid copying (all of the strings are static)
    * qof_book_get_unknown_features returns a FeatureSet

commit e8c80f2f5cca6e16abea87740d59b5b52c9ab69f
Author: John Ralls <jralls at ceridwen.us>
Date:   Fri Apr 28 14:15:59 2023 -0700

    Restore existence, but not implementation, of GNC_FEATURE_BOOK_CURRENCY.
    
    At least one user has managed to get it set on their book so even
    though it was supposed to be unimplemented it got through somehow.
    Restoring it allows books with it set to load.



Summary of changes:
 libgnucash/engine/gnc-features.cpp    | 33 +++++++++++++++++++++++++++++++--
 libgnucash/engine/gnc-features.h      | 11 +++++++++--
 libgnucash/engine/qofbook.cpp         |  6 +++---
 libgnucash/engine/qofbook.hpp         |  5 ++---
 libgnucash/engine/test/test-qofbook.c |  5 +++++
 5 files changed, 50 insertions(+), 10 deletions(-)