Adding full DI navigation example for testing purposes.

- adding internal private field into FormBase class
- adding Extension methods into DependencyInjection namespace for use
- adding 2 NavigateTo extension methods for DI using ServiceProvider
- adding example project
- adding to readme as example

Examples/DependencyInjection/Database/BotDbContext.cs

@@ -0,0 +1,12 @@
+using Microsoft.EntityFrameworkCore;
+
+namespace DependencyInjection.Database;
+
+public class BotDbContext : DbContext
+{
+    public BotDbContext(DbContextOptions options) : base(options)
+    {
+    }
+
+    public DbSet<User> Users { get; set; }
+}

Examples/DependencyInjection/Database/User.cs

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+namespace DependencyInjection.Database;
+
+public class User
+{
+    public long Id { get; set; }
+    public string LastMessage { get; set; }
+}

Examples/DependencyInjection/Forms/ConfirmationForm.cs

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+using DependencyInjection.Database;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using TelegramBotBase.Base;
+using TelegramBotBase.Form;
+using TelegramBotBase.DependencyInjection;
+
+namespace DependencyInjection.Forms
+{
+    public class ConfirmationForm : FormBase
+    {
+        private readonly BotDbContext _dbContext;
+
+        public ConfirmationForm(BotDbContext dbContext)
+        {
+            _dbContext = dbContext;
+        }
+
+        public override async Task Load(MessageResult message)
+        {
+            var user = await _dbContext.Users.FindAsync(Device.DeviceId);
+
+            if (user == null)
+            {
+                await this.NavigateTo<StartForm>();
+                return;
+            }
+        }
+
+        public override async Task Action(MessageResult message)
+        {
+            await message.ConfirmAction("Go back");
+
+            switch (message.RawData)
+            {
+
+                case "back":
+
+                    await this.NavigateTo<StartForm>();
+
+                    break;
+
+            }
+
+
+        }
+
+        public override async Task Render(MessageResult message)
+        {
+            var user = await _dbContext.Users.FindAsync(Device.DeviceId);
+            if (user == null)
+                return;
+
+            var bf = new ButtonForm();
+            bf.AddButtonRow("Back", "back");
+
+            await Device.Send($"ConfirmationForm: Your last message was: {user.LastMessage}. Click \"Back\" to get back.", bf);
+        }
+
+
+
+
+    }
+}

Examples/DependencyInjection/StartForm.cs

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+using DependencyInjection.Database;
+using DependencyInjection.Forms;
+using TelegramBotBase.Base;
+using TelegramBotBase.Form;
+using TelegramBotBase.DependencyInjection;
+
+namespace DependencyInjection;
+
+public class StartForm : FormBase
+{
+    private readonly BotDbContext _dbContext;
+
+    public StartForm(BotDbContext dbContext)
+    {
+        _dbContext = dbContext;
+    }
+
+    public override async Task Load(MessageResult message)
+    {
+        var user = await _dbContext.Users.FindAsync(Device.DeviceId);
+        if (user is null)
+        {
+            user = new User
+            {
+                Id = Device.DeviceId,
+                LastMessage = "<unknown>"
+            };
+
+            _dbContext.Users.Add(user);
+            await _dbContext.SaveChangesAsync();
+        }
+
+        if (message.IsAction)
+            return;
+
+
+        user.LastMessage = string.IsNullOrWhiteSpace(message.MessageText) ? "<unknown>" : message.MessageText;
+        await _dbContext.SaveChangesAsync();
+    }
+
+    public override async Task Action(MessageResult message)
+    {
+        await message.ConfirmAction("Ok");
+
+        switch(message.RawData)
+        {
+
+            case "open":
+
+                await this.NavigateTo(typeof(ConfirmationForm));
+
+                var new_form = await this.NavigateTo<ConfirmationForm>();
+
+                if (new_form == null)
+                {
+                    await Device.Send("Cant open ConfirmationForm");
+                }
+
+                break;
+
+        }
+
+
+    }
+
+    public override async Task Render(MessageResult message)
+    {
+        var user = await _dbContext.Users.FindAsync(Device.DeviceId);
+        if (user == null)
+            return;
+
+        var bf = new ButtonForm();
+
+        bf.AddButtonRow("Open confirmation", "open");
+
+        await Device.Send($"Your last message's text was: `{user.LastMessage}`", bf);
+    }
+
+}