Merge branch 'stable-5.3' into stable-5.4

* stable-5.3:
  Prepare 5.3.9-SNAPSHOT builds
  JGit v5.3.8.202011260953-r
  Prepare 5.1.15-SNAPSHOT builds
  JGit v5.1.14.202011251942-r
  GC#deleteOrphans: log warning for deleted orphaned files
  GC#deleteOrphans: handle failure to list files in pack directory
  Ensure that GC#deleteOrphans respects pack lock
  Update API warning filters
  Remove unused imports

Change-Id: I82576ad0f61cf3ff11b54691b32666c61401ad9b
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

diff --cc org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/dfs/DfsGarbageCollectorTest.java
Simple merge

diff --cc org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties
Simple merge

diff --cc org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java
Simple merge

diff --cc org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/GC.java
Simple merge