Update filter processor to use pdata

[pmcollins]

Updated filter processor to use pdata rather than OC. There's still some OC stuff in filter_processor_test.go, but am hoping that can be updated in a separate change.

Also replaced a benchmark test with a new one. (The previous benchmark test failed with a nil pointer.) The new benchmark test has the following results:

4233112 ns/op before this change
837378 ns/op after this change

[codecov]

Codecov Report

Merging #1885 into master will increase coverage by 0.03%.
The diff coverage is 97.22%.

@@            Coverage Diff             @@
##           master    #1885      +/-   ##
==========================================
+ Coverage   91.30%   91.34%   +0.03%     
==========================================
  Files         280      281       +1     
  Lines       16628    16687      +59     
==========================================
+ Hits        15183    15242      +59     
  Misses       1011     1011              
  Partials      434      434              

Impacted Files	Coverage Δ
processor/filterprocessor/filter_processor.go	90.47% <88.23%> (+1.58%)	⬆️
internal/processor/filtermetric/filtermetric.go	100.00% <100.00%> (ø)
processor/filterprocessor/metric_index.go	100.00% <100.00%> (ø)

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[james-bebbington]

4233112 ns/op before this change
837378 ns/op after this change

Nice 😄

[bogdandrutu]

This is a good solution for the moment, we should maybe think in the future to add helpers filter[Metrics|Logs|Spans] in the future that allows to do this in-place.