Add missing test for data.google_firebase_web_app_config, clean up plugin-framework Firebase code a bit

[SarahFrench]

This PR:

• adds a missing test for the Firebase data sources in the provider
• slightly refactors existing Firebases data sources that have been migrated to the plugin-framework
  • doesn't impact function, instead structures the code differently and adds new comments

Release Note Template for Downstream PRs (will be copied)

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

google provider: Diff ( 1 file changed, 3 insertions(+))
google-beta provider: Diff ( 4 files changed, 77 insertions(+), 21 deletions(-))

[modular-magician]

Tests analytics

Total tests: 18
Passed tests: 14
Skipped tests: 4
Affected tests: 0

Click here to see the affected service packages

• firebase

🟢 All tests passed!

View the build log

[SarahFrench]

Here's a TeamCity build running all Firebase acc tests on this PR's changes: https://hashicorp.teamcity.com/buildConfiguration/TerraformProviders_GoogleCloud_GOOGLE_BETA_MMUPSTREAMTESTS_GOOGLEBETA_PACKAGE_FIREBASE/245968?hideTestsFromDependencies=false&hideProblemsFromDependencies=false&expandBuildChangesSection=true

Edit: all tests passed, including the new TestAccDataSourceGoogleFirebaseWebAppConfig

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

google provider: Diff ( 1 file changed, 3 insertions(+))
google-beta provider: Diff ( 4 files changed, 78 insertions(+), 21 deletions(-))

[modular-magician]

Tests analytics

Total tests: 18
Passed tests: 13
Skipped tests: 5
Affected tests: 0

Click here to see the affected service packages

• firebase

#### Non-exercised tests

Tests were added that are skipped in VCR:

• TestAccDataSourceGoogleFirebaseWebAppConfig
  🟢 All tests passed!

View the build log

[SarahFrench]

Thanks!