Don't consider "unassociated" child content types while matching files

[iloveeclipse]

Fixes #1207

[github-actions]

Test Results

   579 files   -  57     579 suites   - 57   42m 34s ⏱️ -11s
 3 796 tests  - 149   3 762 ✅  - 160   23 💤 ±0  11 ❌ +11 
11 994 runs   - 447  11 797 ✅  - 480  164 💤 ±0  33 ❌ +33 

For more details on these failures, see this check.

Results for commit 3cb1453. ± Comparison against base commit a8f5ea3.

This pull request removes 149 tests.

AllCompareTests org.eclipse.compare.tests.AsyncExecTests ‑ testCancelOnRequeue
AllCompareTests org.eclipse.compare.tests.AsyncExecTests ‑ testQueueAdd
AllCompareTests org.eclipse.compare.tests.AsyncExecTests ‑ testWorker
AllCompareTests org.eclipse.compare.tests.CompareFileRevisionEditorInputTest ‑ testPrepareCompareInputWithNonLocalResourceTypedElements
AllCompareTests org.eclipse.compare.tests.CompareUIPluginTest ‑ testFindContentViewerDescriptorForTextType_StreamAccessor
AllCompareTests org.eclipse.compare.tests.CompareUIPluginTest ‑ testFindContentViewerDescriptor_TextType_NotStreamAccessor
AllCompareTests org.eclipse.compare.tests.CompareUIPluginTest ‑ testFindContentViewerDescriptor_UnknownType
AllCompareTests org.eclipse.compare.tests.ContentMergeViewerTest ‑ testFFFX
AllCompareTests org.eclipse.compare.tests.ContentMergeViewerTest ‑ testFFTX
AllCompareTests org.eclipse.compare.tests.ContentMergeViewerTest ‑ testFFXF
…