replacement for fastled sqrt16() (#4426)

* added bitwise operation based sqrt16

- replacement for fastled, it is about 10% slower for numbers smaller 128 but faster for larger numbers. speed difference is irrelevant to WLED but it saves some flash.

* updated to 32bit, improved for typical WLED use

- making it 32bits allows for larger numbers
- added another initial condition check for medium sized numbers
- increased the "small number" optimization to larger numbers: the function is currently only used to calculate sqrt(x^2+y^2) which even for small segments is larger than the initially used 64, so optimizing for 1024 makes more sense, although the value is arbitrarily chosen

wled00/FX.cpp

@@ -5446,15 +5446,15 @@ uint16_t mode_2Dmetaballs(void) {   // Metaballs by Stefan Petrick. Cannot have
       // and add them together with weightening
       unsigned dx = abs(x - x1);
       unsigned dy = abs(y - y1);
-      unsigned dist = 2 * sqrt16((dx * dx) + (dy * dy));
+      unsigned dist = 2 * sqrt32_bw((dx * dx) + (dy * dy));
 
       dx = abs(x - x2);
       dy = abs(y - y2);
-      dist += sqrt16((dx * dx) + (dy * dy));
+      dist += sqrt32_bw((dx * dx) + (dy * dy));
 
       dx = abs(x - x3);
       dy = abs(y - y3);
-      dist += sqrt16((dx * dx) + (dy * dy));
+      dist += sqrt32_bw((dx * dx) + (dy * dy));
 
       // inverse result
       int color = dist ? 1000 / dist : 255;