cmd/compile: fix late expand_calls leaf type for OpStructSelect/OpArraySelect

For the example in #43551, before late call expansion, the OpArg type is
decomposed to int64. But the late call expansion is currently decompose
it to "x.Key" instead.

This CL make expand_calls decompose further for struct { 1-field type }
and array [1]elem.

This matches the previous rules for early decompose args:

(StructSelect (StructMake1 x)) => x
(ArraySelect (ArrayMake1 x)) => x

Fixes #43551

Change-Id: I2f1ebe18cb81cb967f494331c3d237535d2859e7
Reviewed-on: https://go-review.googlesource.com/c/go/+/282332


Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>