[backport#16106] gui: Sort wallets in open wallet menu

Summary:
https://github.com/bitcoin/bitcoin/pull/16106/commits/224eb9534a8d2b0f140ecb0cc00c61af8ba1da4e

Depends on D6172

Partial backport of Core PR16106

Test Plan:

ninja check
./src/qt/bitcoin-qt -regtest -server
./src/bitcoin-cli -regtest createwallet walletA
./src/bitcoin-cli -regtest createwallet walletB
./src/bitcoin-cli -regtest createwallet walletC

see that all wallets are sorted in 'Open wallet'

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D6174