Update prevector

Summary:

• Backport Core PR14266 : Use initializer instead of initializing fields explicitely in every constructors.
• Backport Core PR14715
• Backport Core PR13711
• Backport Core PR14031
• Backport Core PR14651

Test Plan: Run unit tests with ubsan enabled.

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D3061