internal/civisibility: add support for the test.source.end tag

[tonyredondo]

What does this PR do?

This PR adds a logic to calcule the test.source.end tag with the end line number of a test function using the ast parser. It's a best effort approach, in case we cannot extract it (eg: no source code is available) then we silently bail out.

Motivation

This part of the CI Visibility specs.

Reviewer's Checklist

• Changed code has unit tests for its functionality at or near 100% coverage.
• System-Tests covering this feature have been added and enabled with the va.b.c-dev version tag.
• There is a benchmark for any new code, or changes to existing code.
• If this interacts with the agent in a new way, a system test has been added.
• Add an appropriate team label so this PR gets put in the right place for the release notes.
• Non-trivial go.mod changes, e.g. adding new modules, are reviewed by @DataDog/dd-trace-go-guild.

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