Support for STM32L452

[belnj]

Hi, flash is not supported for STM32L452. I would like to know how to flash it.

[devanlai]

The webstlink source was ported from pystlink before STM32L4 support was added. It looks like pystlink picked up support for it in 2019.

Adding support to webstlink should be possible, though it would involve a bit of porting work to:

1. Port stm32l4.py from Python to JavaScript.
2. Add new STM32L4 device entries from stm32devices.py
3. Add the new STM32L4 flash driver to the list in package.js
4. Add the flash driver name lookup to load_driver() in webstlink.js