Clarify that DI is a type of IoC

The documentation currently states that Inversion of Control (IoC) and
Dependency Injection (DI) are the same thing. Although the two terms
are related, they are not synonymous: DI is a type of IoC.

I believe this change is important because using the terms
interchangeably really muddies the water about the meaning of these two
fundamental concepts of software frameworks.

Closes gh-31679

framework-docs/modules/ROOT/pages/core/beans/introduction.adoc

@@ -2,7 +2,7 @@
 = Introduction to the Spring IoC Container and Beans
 
 This chapter covers the Spring Framework implementation of the Inversion of Control
-(IoC) principle. IoC is also known as dependency injection (DI). It is a process whereby
+(IoC) principle. An important kind of IoC is dependency injection (DI). It is a process whereby
 objects define their dependencies (that is, the other objects they work with) only through
 constructor arguments, arguments to a factory method, or properties that are set on the
 object instance after it is constructed or returned from a factory method. The container