Need to re-visit IsValid handlers for lots of context menu actions

[fuzyll]

Our context menus all over the product (but particularly in the analysis views) are getting very long. Some of these items should just be migrated to hamburger menus (CC Vector35/binaryninja#920), but others just need their IsValid handler to be scoped more appropriately.

Also, CC Vector35/binaryninja#542 for ensuring all of these things can be done via the Command Palette as well.

[plafosse]

Some significant changes were made in > 5.2.8545 This task isn't done as its maybe a never ending task but the list has been shrunk down by 30-40% based on what is in context.