feat!: Move default frontend to src/main

[caalador]

Move frontend folder from root
to src/main.

Closes #18436

[github-actions]

Test Results

1 094 files  ± 0  1 094 suites  ±0   1h 14m 43s ⏱️ - 4m 39s
6 937 tests ± 0  6 888 ✅ ± 0  49 💤 ±0  0 ❌ ±0 
7 278 runs  +11  7 217 ✅ +11  61 💤 ±0  0 ❌ ±0 

Results for commit 8810e09. ± Comparison against base commit 75297ef.

♻️ This comment has been updated with latest results.

[mshabarov]

Some minor comments.

Plus the following leftovers for "frontend" are still there:

• In ExternalDependencyWatcher class the folder is hardcoded
• DeploymentConfigurationFactoryTest the same, "frontend" hardcoded

Also, I tried this change with the hybrid and Flow apps, and it doesn't break them. Nothing is changed and they work as previously.
So in what cases this is a breaking change?
Can we merge this immediately without smart detection?

[caalador]

ExternalDependencyWatcher mentions frontend for metaInfFolder e.g META-INF and not the project frontend folder.
For DeploymentConfigurationFactoryTest the tests mentioning frontend are for the token file contents so the actual folder doesn't matter.

For the unified execution check that the plugin is using the correct code for the frontend folders. it should not work with having frontend in ./frontend

[mshabarov]

LGTM, but I propose to rebase the second PR onto this, and merge the second PR.

Let me test it locally.

[sonarcloud]

Quality Gate passed

Issues
4 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud

[vaadin-bot]

This ticket/PR has been released with Vaadin 24.4.0.