gopls/internal/analysis/gofix: one function per kind

Refactor so that each kind of inlinable (function, type alias, constant)
has its own function for each pass.

Refactoring only; no behavior changes.

For golang/go#32816.

Change-Id: I2f09b4020bcf03409664cee3b8379417d8717fa6
Reviewed-on: https://go-review.googlesource.com/c/tools/+/649456
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Alan Donovan <[email protected]>

Author: jba