feat: introduce :outdated pseudo selector

[nlf]

this adds the :outdated pseudo selector, along with documentation

[npm-cli-bot]

found 20 benchmarks with statistically significant performance improvements

• app-large: clean, lock-only, cache-only, cache-only:peer-deps, modules-only, no-lock, no-cache, no-modules, no-clean, no-clean:audit
• app-medium: clean, lock-only, cache-only, cache-only:peer-deps, modules-only, no-lock, no-cache, no-modules, no-clean, no-clean:audit

timing results

app-large	clean	lock-only	cache-only	cache-only peer-deps	modules-only	no-lock	no-cache	no-modules	no-clean	no-clean audit
npm@8	40.103 ±0.96	20.966 ±0.02	19.046 ±0.10	22.102 ±0.47	3.581 ±0.06	3.635 ±0.19	2.804 ±0.03	13.293 ±0.12	2.797 ±0.02	4.246 ±0.24
#5547	0.128 ±0.00	0.128 ±0.00	0.136 ±0.01	0.126 ±0.00	0.129 ±0.00	0.131 ±0.00	0.126 ±0.00	0.128 ±0.00	0.132 ±0.01	0.125 ±0.00

app-medium	clean	lock-only	cache-only	cache-only peer-deps	modules-only	no-lock	no-cache	no-modules	no-clean	no-clean audit
npm@8	30.443 ±2.75	16.517 ±0.18	14.677 ±0.26	15.540 ±0.31	3.111 ±0.04	3.150 ±0.03	2.923 ±0.04	9.940 ±0.18	2.684 ±0.01	3.590 ±0.07
#5547	0.139 ±0.01	0.127 ±0.00	0.131 ±0.00	0.129 ±0.00	0.128 ±0.00	0.129 ±0.00	0.135 ±0.00	0.126 ±0.00	0.130 ±0.00	0.128 ±0.00

[wraithgar]

Docs update and a take-it-or-leave-it nit.