Fix TomcatEmbeddedServletContainerFactory to set a MERGED_WEB_XML
attribute when JSPs are used. This is required for EL support with
JSPs since Jasper checks the version number in the web.xml. Without
any web.xml Jasper default to disabling EL.
Issue: #55752948
Rework main build POM to be an aggregator pom that does not inherit
from any parent. Introduce new spring-boot-dependencies module to
act as a parent for both spring-boot-starter-parent and
spring-boot-parent.
* For a jar deployment add classpath:static/index.html
(works via Spring MVC mapping)
* For a war the same thing works, but so does adding
index.html to src/main/webapp (works via container
default servlet)
[Fixes#54092261] [bs-252]