Use SkScalar type where appropriate.

Change-Id: Iec4c3dedd0790fc637a914517b2abbb8e303520f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/306320
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>

include/core/SkString.h

@@ -105,7 +105,7 @@ static constexpr int kSkStrAppendScalar_MaxSize = 15;
  *  Thus if the caller wants to add a 0 at the end, buffer must be at least
  *  kSkStrAppendScalar_MaxSize + 1 bytes large.
  */
-char* SkStrAppendScalar(char buffer[], float);
+char* SkStrAppendScalar(char buffer[], SkScalar);
 
 /** \class SkString
 

src/core/SkString.cpp

@@ -150,7 +150,7 @@ char* SkStrAppendS64(char string[], int64_t dec, int minDigits) {
     return SkStrAppendU64(string, udec, minDigits);
 }
 
-char* SkStrAppendScalar(char string[], float value) {
+char* SkStrAppendScalar(char string[], SkScalar value) {
     // since floats have at most 8 significant digits, we limit our %g to that.
     static const char gFormat[] = "%.8g";
     // make it 1 larger for the terminating 0