Signed-off-by: Damien George <damien@micropython.org>

Also known as L2CAP "connection oriented channels". This provides a
socket-like data transfer mechanism for BLE.

Currently only implemented for NimBLE on STM32 / Unix.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

This requires that the event handlers are called from non-interrupt context
(i.e. the MicroPython scheduler).

This will allow the BLE stack (e.g. NimBLE) to run from the scheduler
rather than an IRQ like PENDSV, and therefore be able to invoke Python
callbacks directly/synchronously.  This allows writing Python BLE handlers
for events that require immediate response such as _IRQ_READ_REQUEST (which
was previous a hard IRQ) and future events relating to pairing/bonding.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

So that g++ is not needed to build a non-coverage unix variant.

Signed-off-by: Damien George <damien@micropython.org>

Support building .cpp files and linking them into the micropython
executable in a way similar to how it is done for .c files.  The main
incentive here is to enable user C modules to use C++ files (which are put
in SRC_MOD_CXX by py.mk) since the core itself does not utilize C++.

However, to verify build functionality a unix overage test is added.  The
esp32 port already has CXXFLAGS so just add the user modules' flags to it.
For the unix port use a copy of the CFLAGS but strip the ones which are not
usable for C++.

This commit adds support for using Bluetooth on the unix port via a H4
serial interface (distinct from a USB dongle), with both BTstack and NimBLE
Bluetooth stacks.

Note that MICROPY_PY_BLUETOOTH is now disabled for the coverage variant.
Prior to this commit Bluetooth was anyway not being built on Travis because
libusb was not detected.  But now that bluetooth works in H4 mode it will
be built, and will lead to a large decrease in coverage because Bluetooth
tests cannot be run on Travis.

Previously the interaction between the different layers of the Bluetooth
stack was different on each port and each stack.  This commit defines
common interfaces between them and implements them for cyw43, btstack,
nimble, stm32, unix.

Changes are:
- The default manifest.py is moved to the variants directory (it's in
  "boards" in other ports).
- The coverage variant now uses a custom manifest in its variant directory
  to add frzmpy/frzstr.
- The frzmpy/frzstr tests are moved to variants/coverage/.