Improvements for "Show source"

[MSDN.WhiteKnight]

• Support optional parameters in signature decompiler
• Support source link (browser navigation)
• Support source link (download)
• Correctly handle the last sequence point for C++/CLI symbols
• Don't reload all method's sequence points each time user navigates to previous/next point
• Support decompiling signatures for internalcall or P/Invoke methods
• Syntax highlighting for CIL instructions (in left column)
• Syntax highlighting for displayed source code
• Correctly handle release builds in "Show source (method)" (add {} when they are not included in sequence points)
• Produce proper tokens for generic types, references and pointers in signature decompiler
• Support function pointers in signature decompiler
• MethodSourceViewWindow: button to show whole file with method highlighted
• Support generic constraints
• Support embedded sources in Portable PDB
• Support state machine methods (connect with MoveNext method via StateMachineMethod Table)