Determine the caller pkg path using Go's native package logic

[tabboud]

Before this PR

Inferring the caller pkg path from the filename breaks when repos are not in the GOPATH, such as those that use go modules. See #116 for more information.

After this PR

==COMMIT_MSG==
Use Go's native package logic to determine the caller pkg path and use the GOPATH trimming heuristic as a fallback.
Fixes #116
==COMMIT_MSG==

Possible downsides?

• There are some side affects to using the go package path with modules since the module version will be included github.com/tabboud/test-repo/v2

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This change is 

[changelog-app]

Generate changelog in changelog/@unreleased

Type

• Feature
• Improvement
• Fix
• Break
• Deprecation
• Manual task
• Migration

Description

Use Go's native package logic to determine the caller pkg path and use the GOPATH trimming heuristic as a fallback.
Fixes #116

Check the box to generate changelog(s)

• Generate changelog entry

[tabboud]

See the docs for packages to see where this file=... pattern comes from
https://pkg.go.dev/golang.org/x/tools/go/packages

[tabboud]

I am still testing this out to make sure this is what we want, but opening this up to get some directional feedback. I have noticed that using the resolved package path results in the module version being appending onto the path as well (which is not in the on-disk file path), and may not be ideal for our log filtering by origin.

For example, the following is produced for the following test-repo at v2 module

File: "/Volumes/git/go/src/github.com/tabboud/test-repo/server/server.go"
PkgPath: "github.com/tabboud/test-repo/v2/server"
ModPath: "github.com/tabboud/test-repo/v2"

CallerPkg(0, 1): "github.com/tabboud/test-repo/v2"

Whereas for v1 the following would be produced:

File: "/Volumes/git/go/src/github.com/tabboud/test-repo/server/server.go"
PkgPath: "github.com/tabboud/test-repo/server"
ModPath: "github.com/tabboud/test-repo"

CallerPkg(0, 1): "github.com/tabboud/test-repo"