Add current_time

[bjoernQ]

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Pull Request Details 📖

Description

Closes #1139

This adds time::current_time to get the system uptime.

On ESP32 it uses the (mostly undocumented) LAC timer - same as esp-idf.
On all other chips it uses Systimer.

Testing

The timer_interrupt example is changed to use the API.

I also changed esp-wifi to use it and everything worked fine. (It might also improve performance on Xtensa targets but I didn't benchmark it)

[MabezDev]

I've tried this out locally and all is working fine!

Could we add a small basic test case to assert that current_time increases? I know its simple, but it will at least tell us if for whatever reason (most likely on the esp32) if it broke. Having this break would be pretty bad for esp-wifi :D

[JurajSadel]

LGTM, thanks!

[jessebraham]

Thanks for taking care of this!