Support "go to definition" and "find references" for target names

[harrisont]

Note that both the target's name and the target's output file reference a target.

Places that can define targets:

• Target names
• Copy's .Dest (be sure to correctly handle both file and directory values)
• CopyDir's .Dest?
• ...
• Exec's .ExecOutput
• ...

Places that can reference targets:

• Targets' .PreBuildDependencies
• Copy's .Source
• CopyDir's .SourcePaths?
• ...
• Exec's .ExecInput
• ...
• (unsure) Places that set one the following (defined in FASTBuild's src\Code\Tools\FBuild\FBuildCore\Graph\Node.h):
  • Node::m_PreBuildDependencies
  • Node::m_StaticDependencies
  • Node::m_DynamicDependencies

[harrisont]

Work in progress in branch #5

[harrisont]

Work in progress in branch issue-5.