Add Samba share browse and load content

[cscd98]

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3. If possible try squashing everything in a single commit. This is particularly beneficial in the case of feature merges since it allows easy bisecting when a problem arises

Description

Adds the ability to add act as a samba client. To do so there is new settings under System->Network->SMB Shares to specify IP address, share name, optional username and password etc.

It can connect to a single share, then the user can access that configured shared under "Load Content" to load their ROMs.

It may be needed to load the core first before all related files displayed (e.g. Quake 2 PAK do not get listed until loading core).

1. Adds libsmb2 as a new optional dependency
2. Builds RetroArch with libsmb2 by default if library found on build system (under Ubuntu this is libsmb2-dev), otherwise does not
3. Optionally build deps/libsmb2 per platform, Makefiles require HAVE_BUILTINSMBCLIENT = 1 set. This mode has been tested in 4 and 5.
4. Tested as a client using Ubuntu
5. Tested as a client using webOS using HAVE_BUILTINSMBCLIENT
6. The UWP implementation is untested (I can remove from the PR if required).. I need to spend more time in Windows..

All tests done using a local workgroup, not tested under active directory environment. My server was Ubuntu not Windows.

All code should be protected by HAVE_SMBCLIENT so it should compile cleanly without affecting anything else if disabled.

Portable considerations:

1. In Makefile.common, I have set necessary CFLAGS for building smbclient.
   Normally to build libsmb2 you would run cmake in deps/libsmb2/build to generate: deps/libsmb2/build/config.h, but that doesn't suit the current build system for RetroArch well

2. In the root of deps/libsmb2 there are makefiles targetting different platforms e.g. PS2 etc. I have not explored these as I am just targetting Linux.

Related Issues

#11773
#11518
#8653
#8173

Related Pull Requests

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