See the PR for full details. The updated system will be documented on the website in the near future.

Fix Z-move to uninitialized position in SWITCHING_EXTRUDERS tool_change (no_move=true)

Access to the DWT peripheral for the `CYCCNT` register needs to happen before `main()`. The code needs to be called after the setup of the system clocks, so the right place is between the `premain()` and `main()` function of the STM32 Arduino core.

This patch moves the DWT access code to a new function, which is then placed between `premain()` and `main()`.

Beta testers suggested to adopt the RAMPS order of temperature probe connectors. This commit fixes the order to the RAMPS order.

Responding to #12383

XY probe offsets should be integers because adding decimal points makes the code larger. But if decimals are very much wanted, this commit removes the old restriction.

* Enable SD Card on RepRap Display and RADDS

Define the necessary pins in `pins_RADDS.h` (copied from the `RADDS_DISPLAY` section) for the use of the SD card slot on RRD.

* Make CardReader a static class
* Make CardReader flags into bitfields

* Optimize target_extruder, ignore T with mixing
* Give G-code Tn parity with tool_change

- "old_state" is no longer a class static variable.

* Move special characters to language.h
* Apply some naming standards
* Clean up menu item draw functions
* Rename some Temperature methods
* UI => ExtUI