This reverts commit 930f64689c1fb487714c3836ffa43e49e46aa488 as it's
failing on the Linux bots.

This implements coalescing of progress events using a timeout, as
discussed in the RFC on Discourse [1]. This PR consists of two commits
which, depending on the feedback, I may split up into two PRs. For now,
I think it's easier to review this as a whole.

1. The first commit introduces a new generic `Alarm` class. The class
lets you to schedule a function (callback) to be executed after a given
timeout expires. You can cancel and reset a callback before its
corresponding timeout expires. It achieves this with the help of a
worker thread that sleeps until the next timeout expires. The only
guarantee it provides is that your function is called no sooner than the
requested timeout. Because the callback is called directly from the
worker thread, a long running callback could potentially block the
worker thread. I intentionally kept the implementation as simple as
possible while addressing the needs for the `ProgressManager` use case.
If we want to rely on this somewhere else, we can reassess whether we
need to address those limitations.

2. The second commit uses the Alarm class to coalesce progress events.
To recap the Discourse discussion, when multiple progress events with
the same title execute in close succession, they get broadcast as one to
`eBroadcastBitProgressCategory`. The `ProgressManager` keeps track of
the in-flight progress events and when the refcount hits zero, the Alarm
class is used to schedule broadcasting the event. If a new progress
event comes in before the alarm fires, the alarm is reset (and the
process repeats when the new progress event ends). If no new event comes
in before the timeout expires, the progress event is broadcast.

[1]
https://discourse.llvm.org/t/rfc-improve-lldb-progress-reporting/75717/

Around this time last year, I said on the mailing list [1] that I wanted
to to transform the reproducers into something that resembles a
sysdiagnose on Apple platforms: a collection of files containing a
variety of information to help diagnose bugs or troubleshoot issues.

This patch adds that framework. Based on lessons learned from the
reproducers, I've intentionally tried to keep it small and simple.
Different parts of LLDB can register callbacks (this is necessary for
layering purposes) that will get called when the diagnostics should be
generated.

[1] https://lists.llvm.org/pipermail/lldb-dev/2021-September/017045.html

Differential revision: https://reviews.llvm.org/D134991

This patch removes the remaining reproducer code. The SBReproducer class
remains for ABI stability but is just an empty shell. This completes the
removal process outlined on the mailing list [1].

[1] https://lists.llvm.org/pipermail/lldb-dev/2021-September/017045.html

This patch removes the ability to instantiate the LLDB FileSystem class
with a FileCollector. It keeps the ability to collect files, but uses
the FileCollectorFileSystem to do that transparently.

Because the two are intertwined, this patch also removes the
finalization logic which copied the files over out of process.

This patch removes the ability to instantiate the LLDB FileSystem class
based on a VFS overlay. This also removes the "hack" where we cast the
VFS to a RedirectingFileSystem to obtain the external path. You can
still instantiate a FileSystem with a VFS, but with the caveat that
operations that rely on the external path won't work.

Differential revision: https://reviews.llvm.org/D120923

Most of our code was including Log.h even though that is not where the
"lldb" log channel is defined (Log.h defines the generic logging
infrastructure). This worked because Log.h included Logging.h, even
though it should.

After the recent refactor, it became impossible the two files include
each other in this direction (the opposite inclusion is needed), so this
patch removes the workaround that was put in place and cleans up all
files to include the right thing. It also renames the file to LLDBLog to
better reflect its purpose.

Because of its dependency on clang (and potentially other compilers
downstream, such as swift) lldb_private::GetVersion already lives in its
own library called lldbBase. Despite that, its implementation was spread
across unrelated files. This patch improves things by introducing a
Version library with its own directory, header and implementation file.

The benefits of this patch include:

 - We can get rid of the ugly quoting macros.
 - Other parts of LLDB can read the version number from
   lldb/Version/Version.inc.
 - The implementation can be swapped out for tools like lldb-server than
   don't need to depend on clang at all.

Differential revision: https://reviews.llvm.org/D115211

Replace default bodies of special member functions with = default;

$ run-clang-tidy.py -header-filter='lldb' -checks='-*,modernize-use-equals-default' -fix ,

https://clang.llvm.org/extra/clang-tidy/checks/modernize-use-equals-default.html

Differential revision: https://reviews.llvm.org/D104041