In particular, this fixes the GitBranchContextTest

Now the detector detects only real conflicts, so the test should
prepare real conflicts, not just any merge commit.

- fixed regression: auto-show Docker when the first connection added
- revert for d87abfa6, `doUpdateWindowAvailable` extracted instead
- - super-class logic was based on isAvailable
- - must override whole logic if `hide` does not affect availability

"executeOnPooledThread" runs code in background.
It is OK for production, but not for tests: test may finish before
update and system will report leaked thread because all threads
must be stopped on fixture teardown.

See errors like
"Thread leaked: Thread[BaseDataReader: stdout/stderr streams of shell env loading process,4,main]"

postpone project generator UI instantiation to fix blinking test NewProjectWizardTest.testDefaultLanguageLevel

E.g. NodeJsInterpreterField may spawn "node --version" on its creation which leads to
java.lang.AssertionError: Thread leaked: Thread[BaseDataReader: output stream of /opt/nvm/nvm-wrapper/node --version,4,main]; TIMED_WAITING (true)
--- its stacktrace:
 at java.lang.Object.wait(Native Method)
 at com.intellij.util.io.BaseDataReader.doRun(BaseDataReader.java:175)
 at com.intellij.util.io.BaseDataReader$1$1.run(BaseDataReader.java:66)
 at com.intellij.util.ConcurrencyUtil.runUnderThreadName(ConcurrencyUtil.java:194)
 at com.intellij.util.io.BaseDataReader$1.run(BaseDataReader.java:63)
 at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
 at java.util.concurrent.FutureTask.run(FutureTask.java:266)
 at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
 at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
 at java.lang.Thread.run(Thread.java:745)

1. NavigateFromSourceTest.testShowClassMembers
2. ProjectTreeSortingTest.testFoldersOnTop
3. ProjectTreeSortingTest.testManualOrder
4. ProjectTreeSortingTest.testSortByName
5. ProjectTreeSortingTest.testSortByType
6. ProjectTreeSortingTest.testSortByTypeBetweenFilesAndFolders
7. ProjectViewUpdatingTest.testShowClassMembers
8. ProjectViewUpdatingTest.testStandardProviders
9. ProjectViewUpdatingTest.testUpdateProjectView