Fix rewriter when the sync method is in the same extensions class

[0xced]

Pull request #108 made sure that EF Core async extensions (such as AnyAsync are properly translated to the System.Linq.Queryable.Any extension method).

Unfortunately, this introduced a regression. When async and sync methods are in the same extension class (such as ExecuteDeleteAsync and ExecuteDelete) the generated sync method would be wrong. I.e., generated in System.Linq.Queryable instead of Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.

This pull request tries to address this issue. Unfortunately, I'm again facing discrepancies between the GenerationSandbox.Tests and Generator.Tests projects. This is why this pull request is opened a draft.

When used in the GenerationSandbox.Tests project, the generated code is correct.

// <auto-generated/>
#nullable enable
namespace GenerationSandbox.Tests
{
    public partial class EntityFrameworkQueryableExtensions
    {
        /// <summary>
        /// Test method.
        /// </summary>
        /// <param name="dbContext">The db context.</param>
        /// <returns>The result.</returns>
        public int QueryableExtension(global::Microsoft.EntityFrameworkCore.DbContext dbContext)
        {
            var dbSet = dbContext.Set<object>();
            if (global::System.Linq.Queryable.Any(dbSet))
            {
                return global::Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.ExecuteDelete(dbSet);
            }

            return 0;
        }
    }
}

When generated in the Generator.Tests project, the generated code is incorrect. Note how the
Any and ExecuteDelete methods are not generated with their fully qualified names.

//HintName: Zomp.SyncMethodGenerator.IntegrationTests.EntityFrameworkQueryableExtensions.QueryableExtensionAsync.g.cs
// <auto-generated/>
#nullable enable
namespace Zomp.SyncMethodGenerator.IntegrationTests
{
    public partial class EntityFrameworkQueryableExtensions
    {
        public int QueryableExtension(global::Microsoft.EntityFrameworkCore.DbContext dbContext)
        {
            var dbSet = dbContext.Set<object>();
            if (dbSet.Any())
            {
                return dbSet.ExecuteDelete();
            }
            
            return 0;
        }
    }
}

I don't understand why the generated code is different. I have identified that var symbol = GetSymbol(node) returns null for InvocationExpressionSyntax InvocationExpression dbSet.AnyAsync(cancellationToken) in Generator.Tests and not null in GenerationSandbox.Tests but I don't understand why.