Add AttributesProcessor toString, add attribute filter helper

[jack-berg]

Adds a helper function for specifying that a view should retain only a specific set of attribute keys:
Previous:

Set<String> keysToRetain = new HashSet<>(Arrays.asList("key1", "key2"));
View view = View.builder().setAttributesFilter(keysToRetain::contains);

After:

View view = View.builder().setAttributesFilter(new HashSet<>(Arrays.asList("key1", "key2")));

As an added benefit, we can have ensure a proper toString() implementation when the helper function is used:

Set<String> keysToRetain = new HashSet<>(Arrays.asList("key1", "key2"));
View view = View.builder().setAttributesFilter(keysToRetain::contains);
view.toString(); // View{aggregation=DefaultAggregation, attributesProcessor=AttributeKeyFilteringProcessor{nameFilter=io.opentelemetry.sdk.metrics.ViewTest$$Lambda$405/0x0000000800263508@1dcca8d3}, cardinalityLimit=2000}

View view = View.builder().setAttributesFilter(new HashSet<>(Arrays.asList("key1", "key2")));
view.toString(); // View{aggregation=DefaultAggregation, attributesProcessor=AttributeKeyFilteringProcessor{nameFilter=SetIncludesPredicate{set=[key1, key2]}}, cardinalityLimit=2000}

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (e0a0b77) 91.29% compared to head (93df5ba) 91.30%.
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #5765   +/-   ##
=========================================
  Coverage     91.29%   91.30%           
- Complexity     5245     5256   +11     
=========================================
  Files           585      586    +1     
  Lines         15537    15616   +79     
  Branches       1502     1518   +16     
=========================================
+ Hits          14185    14258   +73     
- Misses          930      931    +1     
- Partials        422      427    +5     

Files Changed	Coverage Δ
...java/io/opentelemetry/sdk/metrics/ViewBuilder.java	91.66% <100.00%> (+1.19%)	⬆️
...sdk/metrics/internal/view/AttributesProcessor.java	77.27% <100.00%> (+8.52%)	⬆️

... and 8 files with indirect coverage changes

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[mateuszrzeszutek]

Can the addAttributesProcessor method be removed? It does not seem to be used anywhere

[jack-berg]

It gets called reflectively by SdkMeterProviderUtil, which provides experimental methods for adding attributes processors which add keys from baggage.

The change here is worth calling out. I've changed the behavior of setAttributeFilter from chaining together to setting the attribute filter, erasing any previous. I believe this is the correct, and is consistent with out places where we have the opportunity to merge or override in a builder. For example, in the Sdk{Signal}ProviderBuilders, we have setResource, which sets the resource, overriding any previously set, and addResource, which merges with the existing.

If generic attribute filters become part of our public API some day, we can consider having both set* and add* variants.