RFR: 7903977: Feature Tests - Fixing TT_SelectionCE test script

[Golla Yadav]

Moved base class "TT_SelectionCE.java" to "jthtest" folder from "TestTree" to avoid the failure and ran all the tests on Linux and Mac machine and its working fine.

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Commit messages:
 - 7903977: Feature Tests - Fixing TT_SelectionCE test script

Changes: https://git.openjdk.org/jtharness/pull/94/files
  Webrev: https://webrevs.openjdk.org/?repo=jtharness&pr=94&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903977
  Stats: 7 lines in 7 files changed: 6 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jtharness/pull/94.diff
  Fetch: git fetch https://git.openjdk.org/jtharness.git pull/94/head:pull/94

PR: https://git.openjdk.org/jtharness/pull/94