std: deprecate ensureCapacity, add two other capacity functions
I've run into this footgun enough times, nearly every time I want
`ensureUnusedCapacity`, not `ensureCapacity`. This commit deprecates
`ensureCapacity` in favor of `ensureTotalCapacity` and introduces
`ensureUnusedCapacity`.
c8ae581fefAndrew Kelley committed on 4/17/2021, 12:56:30 AMparent5ff45b3