Add support for RP2350 (Pico 2)

[pguyot]

Also update OTP matrix for macOS to include OTP27

Also fix build test matrix to also install elixir & rebar3 in all cases.

These changes are made under both the "Apache 2.0" and the "GNU Lesser General
Public License 2.1 or later" license terms (dual license).

SPDX-License-Identifier: Apache-2.0 OR LGPL-2.1-or-later

[bettio]

I'm not sure about the naming here: the day they will add an additional core it will turn into rp3.
Maybe I'd rather call it rpipico or rpico.

[pguyot]

True.

Raspberry Pi had a rp2_common directory before the pico 2.

https://github.com/raspberrypi/pico-sdk/tree/master/src

Micropython calls the port rp2

https://github.com/micropython/micropython/tree/master/ports

I never was a fan of the pico brand name for this platform as pico refers to the board and not the soc and there are a lot of cheap boards using the same soc that we support here.