x/tools/internal/inline: remove dependency on the Go command

[findleyr]

The x/tools source code inliner invokes the Go command indirectly, when it runs goimports logic to compute import edits:
https://cs.opensource.google/go/x/tools/+/master:internal/refactor/inline/inline.go;l=403;drc=39017333097c18f58aa50f00bcd4ce01983ea305

Since the inliner is used in the analysis framework, this is really a violation of boundaries, and causes practical problems when analysis drivers do not have access to the go command for the current environment.

There's also no good reason for this dependency, except that the way goimports is currently factored couples the resolution of imports with the computation of fixes. CC @pjweinb who has also run into this problem while wiring in the modcache index to goimports.

In the short term, we need to remove this dependency from the inliner--even if it means duplicating some logic from goimports.

CC @adonovan @lfolger

[adonovan]

Related:

• x/tools/go/analysis/internal/checker: -fix should remove unneeded imports #72035

If analyzers can rely on -fix to remove unused imports, this task becomes trivial.

[adonovan]

Fixed by @jba in https://go.dev/cl/661635.