Automatically identify the class name based on the specified line number. (#2280)

* identify the scene name based on the line number

* resolving a minor bug in string_mobject

* removing bug of string validation

* Update manimlib/default_config.yml

Co-authored-by: Splines <[email protected]>

* Update manimlib/extract_scene.py

Co-authored-by: Splines <[email protected]>

* update search scene names

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Co-authored-by: Splines <[email protected]>