remove Set.new from DetailsKey::get, impacts rendering overhead performance

Using ruby-prof, I noticed that Set#add had the largest 'self time'
percentage (5% of the overall time spent rendering) when
benchmarking the rendering of a small cached ERB template that was 3
lines long. It turns out it was from this line. I don't believe the
Set is necessary, either. Removing this line increases the rendering
ips using Benchmark::ips accordingly.
Merge pull request #15917 from luke-gru/actionview_perf

remove Set.new from DetailsKey::get, impacts rendering overhead
Use &= instead of select with include?

The performance is almost the same with both implementations but this is
clear.

Before this patch:

Calculating -------------------------------------
  small erb template      1452 i/100ms
-------------------------------------------------
  small erb template    17462.1 (±13.3%) i/s -      85668 in   5.031395s
.Calculating -------------------------------------
small erb template with 1 partial
                           887 i/100ms
-------------------------------------------------
small erb template with 1 partial
                         8899.6 (±18.8%) i/s -      42576 in   5.009453s
.Calculating -------------------------------------
small erb template with 2 partials
                           666 i/100ms
-------------------------------------------------
small erb template with 2 partials
                         6821.5 (±8.8%) i/s -      33966 in   5.020791s

After the patch:

Calculating -------------------------------------
  small erb template      1479 i/100ms
-------------------------------------------------
  small erb template    15956.6 (±7.6%) i/s -      79866 in   5.036001s
.Calculating -------------------------------------
small erb template with 1 partial
                           841 i/100ms
-------------------------------------------------
small erb template with 1 partial
                         9242.2 (±6.9%) i/s -      46255 in   5.029497s
.Calculating -------------------------------------
small erb template with 2 partials
                           615 i/100ms
-------------------------------------------------
small erb template with 2 partials
                         6524.7 (±6.8%) i/s -      32595 in   5.020456s

You can find the benchmark code at
https://gist.github.com/rafaelfranca/dee31120cfdb1ddc3b56
Merge remote-tracking branch 'origin/master'