[NFC] Add SmallVector constructor to allow creation of SmallVector<T> from...

[NFC] Add SmallVector constructor to allow creation of SmallVector<T> from ArrayRef of items convertible to type T

Extracted from https://reviews.llvm.org/D129781 and address comment:
https://reviews.llvm.org/D129781#3655571

Differential Revision: https://reviews.llvm.org/D130268