Document the server mode as deprecated.  Add a deprecation message
to the configure step output when invoked through server mode.

Closes: #19101

Revert commit v3.13.0-rc1~144^2 (cmake-server: Support codemodel
filegroups for INTERFACE_SOURCES, 2018-08-10).  The changes activate
code paths not meant to be used with interface libraries.  Another
approach will be needed to expose this information later.

This revert has to be done by hand because the code in question has been
changed somewhat since the changes were made, and was also factored out
to another source file.

Fixes: #18463

This change returns information for INTERFACE_SOURCES. We add
a flag to the filegroup to indicate if the target represents
interface sources.

Protocol version is updated to 1.3 since this is a change to what was
released in cmake version 3.12.

Document the `=` in the option name.  Clarify the term "named pipe" as
an abstraction of local domain sockets on Unix and named pipes on
Windows.

Document which Protocol version only needs the build directory to be passed
during a handshake.

This is available a bit earlier than that, but from all I can tell 1.2 is
the earliest version where that feature is reliably available.

Some are user-facing. Others are source comments.

Backtrace information was included by commit 35a52bd1 (server: add
"ctestInfo" request to get test info, 2017-10-25) to match that already
provided for targets.  However, the backtrace representation uses too
much memory and needs to be dropped.  Remove it from test information.

Issue: #17502

The backtrace information is very repetitive and hugely increases the
size of the codemodel object.  We need to remove it until an alternative
representation can be developed.  Revert commit v3.10.0-rc1~393^2
(server: Report backtraces in codemodel response, 2017-06-20), except
for the protocol version number (because it indicates other new things).

Unfortunately this is incompatible with clients that expect the
"crossReferences" field in targets.  However, the regression in memory
usage is quite serious, especially on large projects, and therefore
breaks even older clients that do not use backtraces.  Since the
"crossReferences" field was only provided by one release (3.10.0), it is
simplest to revert it outright for 3.10.1.

Fixes: #17502

Some generators auto-generate targets. For example VS generators create
the ALL_BUILD target. Add the ability to mark targets as generator
provided and return that info through cmake-server codemodel.

Prior to this change we were looking at targets. But tests are
associated with directories. This change fixes how we gather all tests.

Protocol version is updated to 1.2 since this is a change
to what was released in cmake version 3.10.

Fixes: #16989

If a required value is in the cache, it is not necessary to set it
explicitly.

Fixes: #16948, #16988

Report the source locations (e.g. in `CMakeLists.txt`) for all targets
and target-related statements.  This allows IDEs to locate the
statements and automatically edit them when the user adds or removes
files or changes target properties via GUI.

Increment the protocol minor version number to tell clients that the new
information is available.

Change our message wrapper from

    [== CMake Server ==[ ... ]== CMake Server ==]

to

    [== "CMake Server" ==[ ... ]== "CMake Server" ==]

to guarantee that no JSON content can ever contain the ending string
(because it would be encoded as `]== \"CMake Server\" ==]`).

Some information was not updated to reflect the latest implementation.
Reported-by: Sylvain Joubert <joubert.sy@gmail.com>

Watch CMakeLists.txt files (and similar) from the Server

* Add a command to report watched files and directories to clients.

With this it would be possible to implement something like
cmake-gui using server-mode.

Add a command to retrieve files that are input to cmake itself.

Add "codemodel" command to report information relevant to feed a code
model.

Add a command to trigger cmake to configure a project.

Keep this separate from the compute step (added in the next commit)
to faciliate applications like cmake-gui.

"setGlobalSettings" can be used to change settings reported by
"globalSettings" command.

Add "globalSettings" command that returns:
* Return capability information
* Return currently used generator/extra generator
* Return a range of flags for debug/trace/etc.

Enable the server to send signals.

Use it to split pipe and stdin/out handling out of cmServer itself.

The server will shut down when it looses its connection to the client.
This has the nice property that a crashing client will cause the server
to terminate as the OS will close the connection on behave of the client.

Enable the server to support development with some helper tools:

You can now request debug information with statistics on how
long execution of a command took, how long it took to serialize
the JSON files, and how big the serialized JSON string is.

Also allow to dump results into a file.

Pass messages sent from cmake via Error(...) or Message(...) on
to clients.