Fix Rails application name and SQL Server check

[aovertus]

Hi,

I've been trying to use the main version of the adapter on our project and can't make it running yet.
Here are 2 issues I've found so far.

1. Small bug

rails_application_name is called on the instance level instead of class

2. Issue with sqlserver? declaration

3.2.0 :001 > User.where(id: 1).exists?
/Users/alexandreovertus/.rvm/gems/ruby-3.2.0/bundler/gems/activerecord-sqlserver-adapter-d1a3b1dd1977/lib/active_record/connection_adapters/sqlserver/core_ext/finder_methods.rb:14:in `construct_relation_for_exists’: undefined method `sqlserver?' for #<ActiveRecord::ConnectionAdapters::Mysql2Adapter:0x0000000117eaf020 @transaction_manager=#<ActiveRecord::ConnectionAdapters::TransactionManager:0x00000001162e0100 @stack=[], @connection=#

sqlserver? is unknown from the other adapter. As I understand the goal of defining a method to easily detect which adapter is currently used rather than relying on the name, its not known by the abstracted layer. Ideally the abstract layer would define a method dynamically based on the name of the adapter, in the meantime we can explicitly add a method on the abstract module to make it shared.

Let me know if it makes sense as if its easier to share those notes or make a useable PR to contribute.

Thanks for your support and help with this library 🎉

[aidanharan]

@aovertus Thanks for the PR! Great to fix the issues you found as soon as possible.