Add Go to Declaration/Implementation/Base/Derived and Navigate To

[pieroviano]

Adds a top-level Navigate menu with go-to commands that act on the symbol under the caret or the selected tree node:

Command	Shortcut
Go to Declaration	F12
Go to Implementation	Ctrl+F12
Go to Base Symbols	Alt+Home
Go to Derived Symbols	Alt+End
Navigate To... (all navigation actions available here)	Ctrl+Shift+G
Analyze (opens the existing Analyze pane)	Shift+F12

• The same entries appear in the code-view and tree context menus.
• Derived symbols and implementations are searched across every loaded assembly that can see the symbol.
• When there are several targets, a searchable chooser opens (type to filter, Up/Down, Enter, Escape). When there are none, a short notice appears.
• Default click behavior is unchanged.

Try it: select a type or put the caret on a member, then Navigate > Go to Implementation (Ctrl+F12).

Split out of #4199 (one feature per PR, as requested there).

Screenshots