Enhance constructor resolution with use of SpEL

[snicoll]

Support of more projects point more and more in the direction of ConstructorResolver that we decided to not include, but rather have a lightweight version of it.

This time, it is a SpEL expression that hides a boolean. The target bean has four constructors and one argument of type String (the spel expression). Two out of the four constructors have a single argument, one is an Executor, and one is a boolean.

We could add a fallback that match the string constructor since, theoretically, the context can convert from one to another anyway.