LibDebug: Add ProcessInspector base class

ProcessInspector is an abstract base class for an object that can
inspect the address space of a process.

Concrete sub classes need to implement methods for peeking & poking
memory and walking the loaded libraries.

It is currently only implemented by DebugSession.

Userland/Libraries/LibDebug/CMakeLists.txt

@@ -9,6 +9,7 @@ set(SOURCES
     Dwarf/DwarfInfo.cpp
     Dwarf/Expression.cpp
     Dwarf/LineProgram.cpp
+    ProcessInspector.cpp
     StackFrameUtils.cpp
 )