runtime: use internal/strconv
Runtime doing its own number formatting dates back to
when runtime was the bottom-most Go package.
Those days are long gone. Use internal/strconv to avoid
duplicating code and also to get better floating-point
formatting:
% go1.24.6 run x.go
+1.
234568e+004
% go run x.go
12345.678
%
With accurate floating point it becomes necessary to
introduce separate printers for float32 vs float64 and
for complex64 vs complex128. Otherwise float32(93.7)
prints as 93.
69999694824219.
Change-Id: I25ae3f09519342dc3d1dcabf4711651423e00128
Reviewed-on: https://go-review.googlesource.com/c/go/+/716002
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>