implement ServerlessServletContext.getResource and ServerlessServletContext.getResourceAsStream

[deki]

After upgrading to Spring Framework 6.2.0 along with Spring Boot 3.4.0 I saw tests failing:

Caused by: java.lang.UnsupportedOperationException: This ServletContext does not represent a running web container
        at org.springframework.cloud.function.serverless.web.ServerlessServletContext.getResource(ServerlessServletContext.java:117)
        at org.springframework.web.context.support.ServletContextResource.getURL(ServletContextResource.java:177)
        at org.springframework.web.servlet.resource.ResourceHandlerUtils.assertResourceLocation(ResourceHandlerUtils.java:67)
        at org.springframework.web.servlet.resource.ResourceHttpRequestHandler.setLocations(ResourceHttpRequestHandler.java:184)
        at org.springframework.web.servlet.config.annotation.ResourceHandlerRegistration.getRequestHandler(ResourceHandlerRegistration.java:239)
        at org.springframework.web.servlet.config.annotation.ResourceHandlerRegistry.getRequestHandler(ResourceHandlerRegistry.java:178)
        at org.springframework.web.servlet.config.annotation.ResourceHandlerRegistry.getHandlerMapping(ResourceHandlerRegistry.java:168)
        at org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport.resourceHandlerMapping(WebMvcConfigurationSupport.java:601)
        at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
        at java.base/java.lang.reflect.Method.invoke(Method.java:580)
        at org.springframework.beans.factory.support.SimpleInstantiationStrategy.lambda$instantiate$0(SimpleInstantiationStrategy.java:171)
        ... 46 more