Find/Replace overlay: consistent handling of incremental base location (#1913 #1914)

[Wittmaxi]

Increment the incremental base location consistently, remove method for
"performIncrementalSearch" as it only called "performSearch" and lead to
semantic confusion while calling "performSearch".

• "SearchOptions.REGEX" will now correctly update the incremental base
  location once it is disabled.
• Added a method for updating the incremental base location manually
  from outside

fixes #1914
fixes #1913
fixes #1915

[github-actions]

Test Results

 1 814 files  +  604   1 814 suites  +604   1h 29m 22s ⏱️ + 22m 18s
 7 666 tests +    3   7 432 ✅ ±    0  233 💤 +  2  1 ❌ +1 
24 114 runs  +8 014  23 364 ✅ +7 777  749 💤 +236  1 ❌ +1 

For more details on these failures, see this check.

Results for commit c087338. ± Comparison against base commit ecfde49.

This pull request skips 5 and un-skips 3 tests.

org.eclipse.ui.genericeditor.tests.HoverTest ‑ testEnabledWhenHover
org.eclipse.ui.genericeditor.tests.HoverTest ‑ testMultipleHover
org.eclipse.ui.genericeditor.tests.HoverTest ‑ testProblemHover
org.eclipse.ui.genericeditor.tests.HoverTest ‑ testSingleHover
org.eclipse.ui.genericeditor.tests.ShowInformationTest ‑ testInformationControl

UiTestSuite org.eclipse.ui.tests.api.ApiTestSuite org.eclipse.ui.tests.api.WorkbenchPluginTest ‑ testGetImageRegistryFromAdditionalDisplay
org.eclipse.jface.text.tests.contentassist.ContextInformationTest ‑ testContextInfo_hide_focusOut
org.eclipse.urischeme.internal.registration.TestUnitWinRegistry ‑ testWinRegistry

♻️ This comment has been updated with latest results.

[HeikoKlare]

I have tested the changes and made two findings:

1. Activating "selection in area" does not work properly anymore
   

2. When deactivating a search option that disables incremental search (in particular regex search) and the currently selected word still matches the search specification, still a new search is triggered, moving the selection to the next match. This behavior already existed before this PR but since this PR affects setting the incremental base position, it should probably be considered here.