Add Bookmarks pad

[siegfriedpammer]

Add a bookmarks pad that allows keeping a list of items from the assembly list treeview for quick navigation.

[greenozon]

Please consider using shortcuts e.g as in VS - F2 and CTRL+F2
devs used to that combo, so will give it a like :)

[wzengguang]

I hope to add bookmark feature. thanks a lot.

[niello]

Bookmarks for individual lines of code will be very useful too

[RTX2080S]

Hello @siegfriedpammer , I can take up this one, just wanted to make sure no one else is working on it right?

[christophwille]

We didn't get around to designing the feature during our developer days. Some notes though:

• What to bookmark: line in decompiled source? Tree nodes?
• What is the identity of the assembly and how do you remember the bookmark (most likely IL to line number in C#) Note: we support not only bog-standard .dll but also eg. NuGet or zipped.
• What happens when the language version changes? Some constructs decompile differently in different language versions and thus the bookmark might shift if C#-line-based.
• What happens to a bookmark if you switch from C# to say IL? Or should we support bookmarks only in C#?
• What happens to a bookmark if you rebuild your project and the line the bookmark was (IL instruction) is no longer there?
• What happens if the assembly is removed from the assembly tree? (most likely: auto-remove all bookmarks, or: have a node with bookmarks for unloaded assemblies so you could get them back if the assembly gets re-added)
• Nice to have "Copy/paste bookmark from assembly x to y" (best effort) - eg you are comparing two assemblies with different versions.
• In the same vein: Export/Import (entire list, bookmarks for assembly) - so one can share bookmarks with others.

In general:

• Do not store in ilspy.xml. Same location, but separate file, eg bookmarks.json.
• Looking at dnSpy visually is ok, source code a big no-no because it is GPL (doesn't mix at all with our MIT license, so best to not know anything about it)