Migrate dd-trace-core groovy files to java part 4 (#11146)

# What Does This Do
we migrate 3 tests:
 - CoreSpanBuilderTest
 - CoreTracerTest
 - DDSpanContextPropagationTagsTest
 
# Motivation
this is part of the effort to migrate groovy tests to Java/JUnit
part1: #11053
part2: #11062
part3: #11085

# Additional Notes

fix some still existing groovy tests regarding ServieNameCollector singleton. see [commit](fcfc49d)

# Contributor Checklist

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- Assign the `type:` and (`comp:` or `inst:`) labels in addition to [any other useful labels](https://github.com/DataDog/dd-trace-java/blob/master/CONTRIBUTING.md#labels)
- Avoid using `close`, `fix`, or [any linking keywords](https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue#linking-a-pull-request-to-an-issue-using-a-keyword) when referencing an issue  
  Use `solves` instead, and assign the PR [milestone](https://github.com/DataDog/dd-trace-java/milestones) to the issue
- Update the [CODEOWNERS](https://github.com/DataDog/dd-trace-java/blob/master/.github/CODEOWNERS) file on source file addition, migration, or deletion
- Update [public documentation](https://docs.datadoghq.com/tracing/trace_collection/library_config/java/) with any new configuration flags or behaviors

Jira ticket: [PROJ-IDENT]

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Co-authored-by: jean-philippe.bempel <jean-philippe.bempel@datadoghq.com>

Author: jpbempel

dd-trace-core/src/test/groovy/datadog/trace/core/CoreSpanBuilderTest.groovy

@@ -696,6 +696,7 @@ class TagInterceptorTest extends DDCoreSpecification {
   }
 
   void "when interceptServiceName extraServiceProvider is called"() {
+    def origServiceNameCollector = ServiceNameCollector.INSTANCE
     setup:
     final extraServiceProvider = Mock(ServiceNameCollector)
     ServiceNameCollector.INSTANCE = extraServiceProvider
@@ -708,9 +709,13 @@ class TagInterceptorTest extends DDCoreSpecification {
 
     then:
     1 * extraServiceProvider.addService("some-service")
+
+    cleanup:
+    ServiceNameCollector.INSTANCE = origServiceNameCollector
   }
 
   void "when interceptServletContext extraServiceProvider is called"() {
+    def origServiceNameCollector = ServiceNameCollector.INSTANCE
     setup:
     final extraServiceProvider = Mock(ServiceNameCollector)
     ServiceNameCollector.INSTANCE = extraServiceProvider
@@ -724,6 +729,9 @@ class TagInterceptorTest extends DDCoreSpecification {
     then:
     1 * extraServiceProvider.addService(expected)
 
+    cleanup:
+    ServiceNameCollector.INSTANCE = origServiceNameCollector
+
     where:
     value   | expected
     "/"     | "root-servlet"

dd-trace-core/src/test/groovy/datadog/trace/core/CoreTracerTest.groovy

@@ -0,0 +1,20 @@
+package datadog.trace.core;
+
+import datadog.trace.api.sampling.PrioritySampling;
+import datadog.trace.api.sampling.SamplingMechanism;
+import datadog.trace.common.sampling.PrioritySampler;
+import datadog.trace.common.sampling.Sampler;
+
+public class ControllableSampler implements Sampler, PrioritySampler {
+  protected int nextSamplingPriority = PrioritySampling.SAMPLER_KEEP;
+
+  @Override
+  public <T extends CoreSpan<T>> void setSamplingPriority(T span) {
+    span.setSamplingPriority(nextSamplingPriority, SamplingMechanism.DEFAULT);
+  }
+
+  @Override
+  public <T extends CoreSpan<T>> boolean sample(T span) {
+    return true;
+  }
+}