flow: Including flow server as a dependency breaks custom spring webmvc configuration

Description of the bug

Merely including flow-server as a dependency breaks custom spring config via @EnableWebMvc

Minimal reproducible example

Here’s a custom webmvc example for serving static resources

@Configuration
@Lazy(false)
@EnableWebMvc
class WebConfiguration : WebMvcConfigurer {
    override fun addResourceHandlers(registry: ResourceHandlerRegistry) {
        super.addResourceHandlers(registry.apply {
            // resource handler for static swagger-ui
            addResourceHandler("/rs/**")
                .addResourceLocations("classpath:/webapp/rs/")

            // resource handler for images
            addResourceHandler("/img/**")
                .addResourceLocations("classpath:/webapp/img/")

            // resource handler for icons
            addResourceHandler("/icon/**")
                .addResourceLocations("classpath:/webapp/icon/")
        });
    }

    override fun addViewControllers(registry: ViewControllerRegistry) {
        super.addViewControllers(
            registry.apply {
                // redirect(s) to index-html
                addRedirectViewController("/rs", "/rs/index.html")
                addRedirectViewController("/rs/", "/rs/index.html")
                addRedirectViewController("/rs/internal", "/rs/internal/index.html")
                addRedirectViewController("/rs/internal/", "/rs/internal/index.html")
            }
        )
    }
}

Expected behavior

Custom webmvc config should not be adversely affected. Also, when not including vaadin-spring or excluding its auto configuration, vaadin should not interfere with spring at all.

Actual behavior

Just by including flow-server as a dependency custom webmvc setup stops working and fetching a static resource will yield:

Resolved [org.springframework.web.HttpRequestMethodNotSupportedException: Request method 'GET' not supported]
15:07:18.006 [mt-6] DEBUG o.s.web.servlet.DispatcherServlet - Completed 405 METHOD_NOT_ALLOWED

Versions:

- Vaadin / Flow version: 17.0.1
- Java version: 14.0.2
- OS version: macos-10.15.6
- Browser version (if applicable): -
- Application Server (if applicable): -
- IDE (if applicable): IJ

Sidenotes

• This issue did not occur with vaadin-14.2.0
• Spring configurations / controllers in non-spring artifact flow-server seem to be misplaced