Well, I figured out why pubspec.yaml and main.dart was not in my project due to the older version of flutter. I downloaded the latest version flutter_windows_2.2.2-stable, created a new flutter project, and included the flutter SDK path of flutter_windows_2.2.2-stable which resolved all my problems. Kindly, make sure whoever wants to start Mobile Application development in Android Studio + Flutter + Dart always download the latest version of everything.
Recent Experiment:
After downloading the latest version of Flutter still, I was unable to get the pubspec.yaml and main.dart files in my Android Studio Project, so the solution is below:
where you have extracted your flutter_windows_2.2.2-stable remember the directory path like E:\src\flutter_windows_2.2.2-stable which is in my scenario.
******************* CMD WORK *******************
Open cmd(Command Prompt) by default you will be in the directory like C:\Users\UserName\
Now go to the path E:\src and to navigate write E: hit enter, now you will be in the E: directory. Write cd E:\src hit enter.
type flutter create project_name ( make sure whenever you withe the name of the project it should be like this my_first_app in this format you name the projects with proper naming convention in flutter [word_word_word_word] ) then hit enter, wait for a while it will create a new flutter project for you including pubspec.yaml and main.dart files + necessary files to be imported.
Reference for naming convention in flutter (https://medium.com/flutter-community/file-and-folder-structure-in-flutter-967b8be3155e#:~:text=Flutter%20doesn't%20have%20a,letters%20and%20underscores%20between%20words.&text=When%20naming%20folders%2C%20you%20want,them%20very%20direct%20and%20clear.)
Right now after the creation of a project(Flutter) in Android Studio you are unable to see/locate the pubspec.yaml and main.dart files use cmd for the project creation which worked in my scenario.