cmd/bundle: add support for embedded generic structs

[norbs57]

The current implementation fails to rename field selectors that refer to embedded generic structs. This commit addresses this issue.

It also replaces calls to the deprecated io/ioutil package with calls to the os package, and there is a code simplification regarding a use of strings.Replace.

Fixes #60647

[gopherbot]

This PR (HEAD: c49f84c) has been imported to Gerrit for code review.

Please visit https://go-review.googlesource.com/c/tools/+/502956 to see it.

Tip: You can toggle comments from me using the comments slash command (e.g. /comments off)
See the Wiki page for more info

[gopherbot]

Message from Gopher Robot:

Patch Set 1:

Congratulations on opening your first change. Thank you for your contribution!

Next steps:
A maintainer will review your change and provide feedback. See
https://go.dev/doc/contribute#review for more info and tips to get your
patch through code review.

Most changes in the Go project go through a few rounds of revision. This can be
surprising to people new to the project. The careful, iterative review process
is our way of helping mentor contributors and ensuring that their contributions
have a lasting impact.

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/502956.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

This PR (HEAD: a014f73) has been imported to Gerrit for code review.

Please visit https://go-review.googlesource.com/c/tools/+/502956 to see it.

Tip: You can toggle comments from me using the comments slash command (e.g. /comments off)
See the Wiki page for more info

[gopherbot]

Message from Alan Donovan:

Patch Set 2:

(4 comments)

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/502956.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

This PR (HEAD: 3a845c4) has been imported to Gerrit for code review.

Please visit https://go-review.googlesource.com/c/tools/+/502956 to see it.

Tip: You can toggle comments from me using the comments slash command (e.g. /comments off)
See the Wiki page for more info

[gopherbot]

Message from tricium-prod@appspot.gserviceaccount.com:

Patch Set 3:

(1 comment)

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/502956.
After addressing review feedback, remember to publish your drafts!