Add isSupported() to firebase/messaging/sw exports

[hsubox76]

Ensures that isSupported() function exported by @firebase/messaging/sw (#4665) is available from firebase/messaging/sw.

Fixes #5309

[changeset-bot]

⚠️ No Changeset found

Latest commit: 5988639

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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[github-actions]

Changeset File Check ⚠️

• Changeset formatting error in following file:

  Package "firebase-compat-typings-test" must depend on the current version of "firebase-exp": "9.0.0-beta.8" vs "file:../../packages-exp/firebase-exp"
  Package "firebase-compat-typings-test" must depend on the current version of "firebase-exp": "9.0.0-beta.8" vs "file:../../packages-exp/firebase-exp"
  Package "firebase-compat-typings-test" must depend on the current version of "firebase-exp": "9.0.0-beta.8" vs "file:../../packages-exp/firebase-exp"
  Some packages have been changed but no changesets were found. Run `changeset add` to resolve this error.
  If this change doesn't need a release, run `changeset add --empty`.
  

[google-oss-bot]

Binary Size Report

Affected SDKs

No changes between base commit (f825b1d) and head commit (217bf0d).

Test Logs

• Base (f825b1d8): https://github.com/firebase/firebase-js-sdk/actions/runs/1140078411
• Head (217bf0d1): https://github.com/firebase/firebase-js-sdk/actions/runs/1140200182

[google-oss-bot]

Size Analysis Report

Affected Products

No changes between base commit (f825b1d) and head commit (217bf0d).

Test Logs

• Base (f825b1d): https://github.com/firebase/firebase-js-sdk/actions/runs/1140078411
• Head (217bf0d): https://github.com/firebase/firebase-js-sdk/actions/runs/1140200182