drivers/led: add LED_NUMOF and convenience inline functions

[mguetschow]

Contribution description

While reviewing #20782, I found some expected convenience functions for simple LED usage to be missing from "led.h". This PR adds the following:

• a macro LED_NUMOF that provides the number of available LEDs at compile-time
• static inline convenience functions led_{on,off,toggle} with the LED id as run-time argument, mirroring the LED_{ON,OFF,TOGGLE} compile-time macros

Also adapts tests/leds to (partly) use the newly provided functionality.

Testing procedure

make -C tests/leds should still work with the board of your choice.

Issues/PRs references

Could enable an easier application code for examples like #20782

[riot-ci]

Murdock results

✔️ PASSED

bb97445 boards/*: include periph/gpio.h in board.h

Success	Failures	Total	Runtime
146563	0	146563	03h:31m:28s

Artifacts

• Documentation preview

[benpicco]

Nice addition.

[benpicco]

Can we add this to led.h instead to avoid changing all board definitions?

[mguetschow]

Well we could, but if we want to follow the include-what-you-use paradigm (see #20570), it doesn't make sense to add it to led.h. That file does not use the content of periph/gpio.h, while the board.h files indeed do (e.g., GPIO_PIN).

[mguetschow]

For example, running make -C examples/hello-world BOARD=adafruit-grand-central-m4-express all with the following diff also fails on master due to the missing include in board.h, completely independent of led.h:

diff --git a/examples/hello-world/main.c b/examples/hello-world/main.c
index 213128ac64..a34fcc00bf 100644
--- a/examples/hello-world/main.c
+++ b/examples/hello-world/main.c
@@ -21,6 +21,8 @@
 
 #include <stdio.h>
 
+#include "board.h"
+
 int main(void)
 {
     puts("Hello World!");
@@ -28,5 +30,7 @@ int main(void)
     printf("You are running RIOT on a(n) %s board.\n", RIOT_BOARD);
     printf("This board features a(n) %s CPU.\n", RIOT_CPU);
 
+    printf("board.h defined PIN: %d\n", WS281X_PARAM_PIN);
+
     return 0;
 }

This now only gets apparent because the macros are used in the inline functions.

But anyway, I feel like the board.h include structure could benefit from a bigger overhaul in any case, so I'm not too strictly opposed to put the include in led.h instead for now. What do you think?