Move two member completion tests to the end-to-end tier

[Firehed]

Summary

Stacked on #686.

A proof of concept for moving member completion onto the end-to-end tier, with two cases from CompletionHandlerIntegrationTest:

• $this-> in a class with a three-level ancestry offers its own members and every ancestor's.
• Static access from an unrelated class offers only public static members.

Each script's Offers and Withholds expectations are the original's assertions, label for label.

The two original tests are removed, so this shows a migration end to end. Coverage is unchanged, file by file. The rest of the completion suite is not moved here.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.67%. Comparing base (9ea8e79) to head (ea4e1d5).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@                     Coverage Diff                     @@
##             e2e-hover-signature-help     #687   +/-   ##
===========================================================
  Coverage                       99.67%   99.67%           
  Complexity                       1900     1900           
===========================================================
  Files                             135      135           
  Lines                            4873     4873           
===========================================================
  Hits                             4857     4857           
  Misses                             16       16           

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