refactor(core): Use (tree-shakeable) string constants for semconv

[JohannesHuster]

Which problem is this PR solving?

Updates #4567

Short description of the changes

Replace deprecated imports from “@opentelemetry/semantic-conventions” with new (tree-shakeable) string constants for core package. What I did:

• Search for “@opentelemetry/semantic-conventions” in package path.
  • Add new imports and check that new and old strings match exactly.
  • Use new imports and remove old ones.

Type of change

• Bug fix (non-breaking change which fixes an issue) (refactor)

How Has This Been Tested?

• npm test

Checklist:

• Followed the style guidelines of this project
• Unit tests have been added
  • No new functionality
• Documentation has been updated
  • I'm not sure if documentation, like described in Document instrumentation semantic conventions opentelemetry-js-contrib#1778, is wanted for this package at the moment. Please let me know, if I should add it.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: JohannesHuster / name: Johannes Huster (6cffd7f, 8db2c3e)