Initial contribution of MethodHandle documentation

This commit contributes documentation that gives an overview
of MethodHandles and VarHandles, and how it is implemented
in the OpenJ9 JIT. The documentation covers the
compilation pipeline from IL generation through optimization
passes to code generation, focusing on the OpenJDK MethodHandle
implementation used in Java 17+. It includes detailed explanations
of key components such as MethodHandleTransformer, Known Object
Table integration, call refinement strategies, inliner support,
and VarHandle related optimizations.

Assisted-by: IBM Bob
Co-authored-by: Nazim Bhuiyan <nubhuiyan@ibm.com>
Signed-off-by: Saad Younus <saad.younus@ibm.com>

Author: saad-ibm