Platform improvements

[mrexodia]

Just added a few APIs I needed while writing a simple plugin to map a file into memory:

using System;
using Dotx64Dbg;

public partial class MyPlugin : IPlugin, IHotload
{
    /// <summary>
    /// Called as soon the plugin is first loaded, consequent hot-loads will not call this again.
    /// </summary>
    public MyPlugin()
    {
        Console.WriteLine("Hello World");
    }

    [UI.Menu(UI.Menu.Root.MemoryMap, "Map file")]
    public void MapFile()
    {
        var file = Platform.OpenFileBrowse("Select a file to map", "All files (*.*)");
        if(string.IsNullOrEmpty(file))
            return;
        
        var data = System.IO.File.ReadAllBytes(file);
        var page = Memory.RemoteAlloc(0, data.Length);
        if(page == 0)
        {
            Platform.MessageBoxError("Failed to allocate memory");
            return;
        }

        if(Memory.Write(page, data) != data.Length)
        {
            Platform.MessageBoxError("Failed to write memory");
            return;
        }

        UI.MemoryMap.Update();
        var ptr = "0x" + page.ToString("X");
        Platform.SetClipboardText(ptr);
        Platform.MessageBoxInfo($"File mapped to: {ptr} (address copied to clipboard)");
        UI.MemoryMap.SetSelection(new UI.Selection(page, page));
    }

    /// <summary>
    /// This is called after construction. This is also only called once.
    /// </summary>
    public void Startup()
    {
    }

    /// <summary>
    /// Classes that  have IHotload can implement this to get a notification for whenever
    /// the plugin was hot-loaded due to changes. This is not called for the startup.
    /// </summary>
    public void OnHotload()
    {
    }

    /// <summary>
    /// This is called right before the plugin is about to be shutdown.
    /// </summary>
    public void Shutdown()
    {
    }
} 

We should probably allow flattening the menus btw. I think if a plugin has a single menu entry it can all just be added directly to the context menu instead of the indirections there are now...

[ZehMatt]

Needs the CI fixed otherwise looking good.