fix: respect sampled flag in Span Processors, fix associated tests

[quickgiant]

Which problem is this PR solving?

Fixes #2394

Short description of the changes

Span Processor classes were missing a check on trace flags to determine whether spans are sampled and should be exported, as per the spec here: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/trace/sdk.md#sampling. These classes originally performed this check and in the case of SimpleSpanProcessor, there is actually a unit test for the behavior that was incorrectly passing due to an issue regarding a shared exporter instance across tests. Since the shared exporter was shut down in the first test, the unsampled span was being dropped, causing the test to pass for the wrong reason.

This change restores the trace flags checks, fixes the SimpleSpanProcessor test, and adds a new test for BatchSpanProcessor. No change is needed for MultiSpanProcessor because the individual span processors ought to do the checks themselves.

[linux-foundation-easycla]

The committers are authorized under a signed CLA.

• ✅ Clark Jacobsohn (5481af4)

[codecov]

Codecov Report

Merging #2396 (0b1748f) into main (f180870) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #2396      +/-   ##
==========================================
- Coverage   92.80%   92.79%   -0.02%     
==========================================
  Files         145      145              
  Lines        5226     5230       +4     
  Branches     1071     1073       +2     
==========================================
+ Hits         4850     4853       +3     
- Misses        376      377       +1     

Impacted Files	Coverage Δ
...dk-trace-base/src/export/BatchSpanProcessorBase.ts	91.57% <100.00%> (+0.18%)	⬆️
...y-sdk-trace-base/src/export/SimpleSpanProcessor.ts	83.87% <100.00%> (+1.11%)	⬆️
...emetry-core/src/platform/node/RandomIdGenerator.ts	87.50% <0.00%> (-6.25%)	⬇️

[obecny]

lgtm

[Flarna]

@quickgiant Please avoid forced pushes as this makes reviewing of changes harder. It's fine to add a lot commits and merge main as needed. During integration to main all commits on your branch will be squashed into a single one.