Add UART support to STM32 platform

[pguyot]

Continuation of:

• Add UART support to RP2 platform #2125
• Add SPI support to STM32 platform #2127

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

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