As the docs say, "If timely disposal of file system resources is
required, the try-with-resources construct should be used to ensure
that the stream's close method is invoked after the stream operations
are completed."

Turns out that without closing the stream, the JVM runs out of memory
pretty quickly. Doing this is not optional but mandatory.

Implements #25307.

Implements #25309.

Part of #20542.

Part of #20542.

Part of #20542.

Replace all File references with their Path equivalents, and use Files
methods wherever feasible.

Part of #20542.

The separation between BridgeSnapshotReader, BridgeDescriptorParser,
and SanitizedBridgesWriter doesn't make much sense anymore:

 - BridgeSnapshotReader only has a constructor of more than 200 lines
   of code.

 - BridgeDescriptorParser actually only determines the descriptor type
   and

 - SanitizedBridgesWriter performs parsing and obfuscation.

There are better ways to structure this code. The first step in that
direction is to remove clutter by moving the code to read bridge
snapshots to SanitizedBridgesWriter and deleting the other two
classes.

Part of #20542.

The indexer did not handle a (mostly theoretic) edge case of a file
being moved away and then moved back shortly after. In such a case the
file should not be marked for deletion anymore and it should be
included in the index again. That's what this commit does.

The other minor changes to unit tests are just cosmetic.

Fixes #34030.

One of the previously made changes to cleaning up directories was that
empty directories were deleted. This was necessary, because otherwise
there would be a growing number of directories as files get deleted
after reaching an age of seven weeks.

However, this change should not have included deleting the cleaned up
directory itself. In practice, this will not happen. But in tests it's
certainly possible that a directory is empty and then gets deleted.
This leads to all sorts of problems in tests.

The fix is to limit deleting empty directories to subdirectories.
That's what this commit does.

Fixes #21219.

These lines have been added by proposal 313 and are usually not
included by bridges. But apparently some bridges include them anyway,
probably bridges that have been configured as non-bridge relays
before. We should retain them just like we retain other statistics
lines.

Implements #34072.

Fixes #19828.

Part of #33655.

Implements #33549.

This was accidentally broken in #32554. The RunOnce mode worked just
fine, but the non-RunOnce mode terminated immediately after scheduling
tasks.