Reimplement SD.h write methods exactly in File (#5861)

* Reimplement SD.h write methods exactly in File

Replace the individual override with the existing SD.h File's
implementation for all methods of File::write.

Fixes #5846

* Add add'l tests

* Fix Print and File incompatible writes w/casts

Print and File have ambiguous resolutions for single-argument
write(0)s.

Fix by adding explicit methods.  A write of any integer will not be a
const char* write (i.e. won't write a string) but will instead just
write the integer truncated to 8 bits (as makes sense).

* Use 256byte chunks in ::write template

Reduce stack requirements for templated writes to 256bytes, matching the
size uses in WiFiClient/etc. (from 512bytes).  Reduces the chance of
stack overflow.

* Move write(int) methods up to Print.h

Remove some technical debt by moving the ::write(int/short/long) methods
out of FS and HardwareSerial and up into Print.h.

cores/esp8266/HardwareSerial.h

@@ -152,22 +152,6 @@ public:
     {
         return uart_write_char(_uart, c);
     }
-    inline size_t write(unsigned long n)
-    {
-        return write((uint8_t) n);
-    }
-    inline size_t write(long n)
-    {
-        return write((uint8_t) n);
-    }
-    inline size_t write(unsigned int n)
-    {
-        return write((uint8_t) n);
-    }
-    inline size_t write(int n)
-    {
-        return write((uint8_t) n);
-    }
     size_t write(const uint8_t *buffer, size_t size) override
     {
         return uart_write(_uart, (const char*)buffer, size);