fmt: refactor pointer formatting and improve tests
Uses a switch statement for direct format function selection
similar to other types verb handling in fmt.
Applies padding also to nil pointers formatted with %v.
Guards against "slice bounds out of range" panic in TestSprintf
when a pointer test results in a formatted string s
that is shorter than the index i the pointer should appear in.
Adds more and rearranges tests.
Fixes #14712
Fixes #14714
Change-Id: Iaf5ae37b7e6ba7d27d528d199f2b2eb9d5829b8c
Reviewed-on: https://go-review.googlesource.com/20371
Run-TryBot: Rob Pike <r@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Rob Pike <r@golang.org>