refactor!: isolate CssImport styles within exported web component

[vursen]

Description

WIP

Fixes #21272

Type of change

• Refactor

[sonarqubecloud]

Quality Gate passed

Issues
8 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

Test Results

1 197 files   -  17  1 197 suites   - 17   1h 10m 55s ⏱️ - 8m 32s
8 241 tests  - 115  8 153 ✅  - 147  55 💤  - 1  33 ❌ +33 
8 633 runs   - 133  8 536 ✅  - 165  64 💤  - 1  33 ❌ +33 

For more details on these failures, see this check.

Results for commit c40eaf9. ± Comparison against base commit ba644ca.

This pull request removes 115 tests.

com.vaadin.base.devserver.AbstractDevServerRunnerTest ‑ shouldPassEncodedUrlToDevServer
com.vaadin.base.devserver.AbstractDevServerRunnerTest ‑ updateServerStartupEnvironment_preferIpv4_LocalhostIpAddressAddedToProcessEnvironment
com.vaadin.base.devserver.AbstractDevServerRunnerTest ‑ updateServerStartupEnvironment_preferIpv6_LocalhostIpAddressAddedToProcessEnvironment
com.vaadin.base.devserver.BrowserLiveReloadAccessorImplTest ‑ getLiveReload_devMode_contextHasNoReloadInstance_instanceIsCreated
com.vaadin.base.devserver.BrowserLiveReloadAccessorImplTest ‑ getLiveReload_devMode_contextHasReloadInstance_instanceIsReturned
com.vaadin.base.devserver.BrowserLiveReloadAccessorImplTest ‑ getLiveReload_liveReloadDisabled_instanceIsCreated
com.vaadin.base.devserver.BrowserLiveReloadAccessorImplTest ‑ getLiveReload_productionMode_nullIsReturned
com.vaadin.base.devserver.DebugWindowConnectionTest ‑ backwardsCompatibilityClassExists
com.vaadin.base.devserver.DebugWindowConnectionTest ‑ getBackend_HotSwapVaadinIntegrationClassLoaded_returnsHOTSWAP_AGENT
com.vaadin.base.devserver.DebugWindowConnectionTest ‑ getBackend_JRebelClassEventListenerClassLoaded_returnsJREBEL
…