Label matcher optimizations

[MasslessParticle]

These are some low-hanging optimizations to regex label matchers that already exist for our line-filter matchers:

• Replace .* matchers with a noop
• Replace .+ with `len(value) > 0
• Rewrite greedy regexes to be non-greedy
• replace literals with strings.Contain

Benchmarks:

Replace .* with noop
name            old time/op    new time/op    delta
EmptyFilters-8    45.2ns ± 3%     1.8ns ± 3%  -95.93%  (p=0.000 n=8+8)

name            old alloc/op   new alloc/op   delta
EmptyFilters-8     0.00B          0.00B          ~     (all equal)

name            old allocs/op  new allocs/op  delta
EmptyFilters-8      0.00           0.00          ~     (all equal)

Replace .+ with len > 0
name             old time/op    new time/op    delta
ExistsFilters-8    10.6ns ±13%     4.5ns ± 8%  -57.78%  (p=0.000 n=10+10)

name             old alloc/op   new alloc/op   delta
ExistsFilters-8     0.00B          0.00B          ~     (all equal)

name             old allocs/op  new allocs/op  delta
ExistsFilters-8      0.00           0.00          ~     (all equal)

Replace literal with strings.Contain
name              old time/op    new time/op    delta
LiteralFilters-8    10.6ns ± 8%     6.0ns ± 1%  -43.50%  (p=0.000 n=10+8)

name              old alloc/op   new alloc/op   delta
LiteralFilters-8     0.00B          0.00B          ~     (all equal)

name              old allocs/op  new allocs/op  delta
LiteralFilters-8      0.00           0.00          ~     (all equal)

greedy -> non-greedy optimizations are benchmarked in this PR: #4775

[owen-d]

LGTM, looks great.

[MasslessParticle]

This draft is superseded by: #8659 which reuses our optimized line filters as label filters.