Fix error issues reported by phpStan level2 tool

[thanhnd0905]

Description

Fixes: https://app.asana.com/0/1204419514580775/1206148918307666

There are 1598 errors when upgrade phpStan level to 2
See here: https://gist.github.com/thanhnd0905/d1dc17e8fe10d8a56e7456444b6f1943

Below are the commits for fixing all errors for each folder:
Fix error issues reported by PhpSta level2 tool in API folder
Fix error issues reported by PhpSta level2 tool in Block folder
Fix error issues reported by PhpSta level2 tool in Controller folder
Fix error issues reported by PhpSta level2 tool in Observer folder
Fix error issues reported by PhpSta level2 tool in Helper folder
Fix error issues reported by PhpSta level2 tool in Model folder
Fix error issues reported by PhpSta level2 tool in Plugin folder
Fix error issues reported by PhpSta level2 tool in ThirdPartyModules folder

#changelog Fix error issues reported by PhpSta level2 tool in API folder

Type of change

• Bug fix (change which fixes an issue)
• New feature (change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please validate that you have tested your change in at least one of the following areas:

• Successfully tested locally (or docker image)
• Successfully tested on a staging or sandbox server
• Successfully tested on a merchant's staging server

For PR Reviewer

• Reviewed unit tests to make sure we are using real components rather than mocks as much as possible?
• For any major change (observer, new Bolt feature, core Magento interaction) we must add a feature switch, did you verify this?

Checklist:

• My code follows the style guidelines of this project.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• New and existing unit tests pass locally with my changes.
• I have created or modified unit tests to sufficiently cover my changes.
• I have added my ticket link and provided a changelog message.

[peril-bolt]

	Warnings
⚠️	Plugin directory has been modified - please take extra care reviewing overwritten core M2 classes.
⚠️	Helper/Config.php has been changed - please make sure you have updated getAllConfigSettings.

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