Use sprintf to output floats in Print/dtostrf

[earlephilhower]

Fixes #7043

Two slightly different custom routines were implemented by hand in
dtostrf (an AVR-lib non-ISO function) and Print. This resulted in
inconsistent output of float/double vars when rounding was needed.

Replace them all with a call to sprintf(), removing the duplicated, not
quite correct code.

Print(String(float)) and Print(float) now generate the same output.

[earlephilhower]

The example code in the original bug (with an INF and NAN added for checks) now reports the same results no matter if it's Print(float) or Print(String(float)):

#include <Arduino.h>

void setup() {
  Serial.begin(115200);
  while (!Serial) yield(); 
  int a = 1014;
  float b = 1014.45;
  double c = 1014.5;

  Serial.println();
  Serial.println(a);
  
  Serial.println();
  Serial.println(b, 1);
  Serial.println(b, 2);
  Serial.println(String(b,1));

  Serial.println();
  Serial.println(c, 0);
  Serial.println(String(c ,0));

  float n = nanf("x");
  Serial.println(n);

  float u = 1/0.0;
  Serial.println(u);

}

void loop() {
}

1014

1014.5
1014.45
1014.5

1014
1014
nan
inf

[mcspr]

Might need to be labelled as breaking? See
https://github.com/arendst/Tasmota/blob/1598e6227a31be5f27081c5a660d22d21613c0ca/platformio.ini#L83
https://github.com/arendst/Tasmota/blob/development/pio/strip-floats.py
https://github.com/xoseperez/espurna/blob/dev/code/scripts/espurna_utils/float_support.py

It removes -u _printf_float from linker flags, so this might come as a surprise b/c code uses dtostrf routinely :)

[earlephilhower]

Ah, crap. Thank you for reminding me about that! I had a niggle about it, but it's been maybe 2 years since the whole -u print_float stuff.

I'll open a new issue. The solution is not clear to me now.