runtime: use dedicated printfloat32

It can be unexpected that printing a float32 involves 64-bit floating
point routines, see for example:
https://github.com/tinygo-org/tinygo/issues/1415

This commit adds a dedicated printfloat32 instead just for printing
float32 values. It comes with a possible code size increase, but only if
both float32 and float64 values are printed. Therefore, this should be
an improvement in almost all cases.

I also tried using printfloat32 for everything (and casting a float64 to
float32 to print) but the printed values are slightly different,
breaking the testdata/math.go test for example.

testdata/print.go

@@ -29,6 +29,9 @@ func main() {
 	// print float64
 	println(3.14)
 
+	// print float32
+	println(float32(3.14))
+
 	// print complex128
 	println(5 + 1.2345i)
 

testdata/print.txt

@@ -16,6 +16,7 @@ a b c
 123456789012
 -123456789012
 +3.140000e+000
++3.140000e+000
 (+5.000000e+000+1.234500e+000i)
 (0:nil)
 map[2]