fix: clean up devtools frontend_host on webcontents destroy

[albertxing]

Description of Change

Fixes #40660

Re-using the previous DevToolsFrontendHost instance no longer works, so we need to clean it up when devtools is closed.
Also updates IsInMainFrame to IsInPrimaryMainFrame to match upstream changes: https://chromium-review.googlesource.com/c/chromium/src/+/2957195

Checklist

• PR description included and stakeholders cc'd
• npm test passes
• tests are changed or added
• PR release notes describe the change in a way relevant to app developers, and are capitalized, punctuated, and past tense.

Release Notes

Notes: Fixed an issue where devtools could not be re-opened.

[welcome]

💖 Thanks for opening this pull request! 💖

We use semantic commit messages to streamline the release process. Before your pull request can be merged, you should update your pull request title to start with a semantic prefix.

Examples of commit messages with semantic prefixes:

• fix: don't overwrite prevent_default if default wasn't prevented
• feat: add app.isPackaged() method
• docs: app.isDefaultProtocolClient is now available on Linux

Things that will help get your PR across the finish line:

• Follow the JavaScript, C++, and Python coding style.
• Run npm run lint locally to catch formatting errors earlier.
• Document any user-facing changes you've made following the documentation styleguide.
• Include tests when adding/changing behavior.
• Include screenshots and animated GIFs whenever possible.

We get a lot of pull requests on this repo, so please be patient and we will get back to you as soon as we can.

[welcome]

Congrats on merging your first pull request! 🎉🎉🎉

[release-clerk]

Release Notes Persisted

Fixed an issue where devtools could not be re-opened.

[trop]

I have automatically backported this PR to "28-x-y", please check out #40679