PR: Define Switcher Plugin public API + fix switcher position bug

[AngelaRemolina]

Description of Changes

• Implemented the plublic API for the Switcher Plugin.
• Fixed the bug occurring with the position of switcher in an editor new window.
• Moved back the EditorSwitcherManager from spyder/plugins/switcher/ to spyder/plugins/editor/utils/ and rename it from manager.py to switcher_manager.py

• Wrote at least one-line docstrings

• Included a screenshot or animation

Issue(s) Resolved

Continue PR #20714
Necessary to solve #3860

Affirmation

By submitting this Pull Request or typing my (user)name below,
I affirm the Developer Certificate of Origin
with respect to all commits and content included in this PR,
and understand I am releasing the same under Spyder's MIT (Expat) license.

I certify the above statement is true and correct: @angelasofiaremolinagutierrez

[ccordoba12]

Great work @angelasofiaremolinagutierrez! I left some minor suggestions for you and a couple of questions, the rest looks pretty good to me.

[dalthviz]

Thanks for all the work here @angelasofiaremolinagutierrez ! Left some comments regarding methods that could be part of the plugin (open_switcher and open_symbolfinder), some info about the on_close method that the plugin or container can implement, and an attribute that seems like could be removed (self._modes at the plugin on_initialize).

If you have any question about the above or something else lets us know!

[dalthviz]

Thanks @angelasofiaremolinagutierrez !

[ccordoba12]

Looks good to me too, thanks @angelasofiaremolinagutierrez!