Co-authored-by: Scott Lahteine <thinkyhead@users.noreply.github.com>

Fix #16881

Allow `ENABLED`, `DISABLED`, `PIN_EXISTS`, and `BUTTON_EXISTS` to take multiple arguments. Also add:
- Alias `ANY(...)` for `!DISABLED(...)`
- Alias `ANY_PIN(...)` for `PIN_EXISTS(a) || PIN_EXISTS(b) ...`
- Alias `EITHER(A,B)` for `ANY(...)`
- Alias `ALL(...)` and `BOTH(A,B)` for `ENABLED(...)`
- `NONE(...)` for `DISABLED(...)`

These values are always supplied by `Conditionals_post.h`.

* Apply #pragma once in headers
* Adjust some thermistors formatting
* Misc cleanup and formatting

- Drop `pgm_read_*_near` and let headers choose.
- Define `USE_EXECUTE_COMMANDS_IMMEDIATE` as a conditional.
- Add `process_subcommands_now` for SRAM-based commands.

Co-Authored-By: TheLongAndOnly <thelongandonly@users.noreply.github.com>

When possible, make `active_extruder` a `constexpr` to save some PROGMEM.