Merge #12035: [qt] change µBTC to bits

Summary:
ebcee1de2 bips: add bip176 (Bits Denomination) (William Casarin)
275b2eeed [qt] change µBTC to bits (William Casarin)

Pull request description:

Now that we have bip176, change "µBTC" to the more colloquial "bits"

Tree-SHA512: eba5e5f89c392728a4f0a3bd81a9779a117b8d72a490390fd031d4e7cc56c2bfee0016aba7ef9535903e8cf2262ce46497283424e378906d0e3bf5b0d2d981c7

Backport of Core PR12035

The naming changes were excluded.

Test Plan:

ninja
./bitcoin-qt

Options -> Display -> Units -> µBTC
Verify home screen displays proper units.

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, jasonbcox

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, jasonbcox

Subscribers: jasonbcox, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D5296