[Core Fix] add loadstore back

[Jim8y]

Description

This pr focus on adding LoadStore back as it was removed by silly me. Plugins still need it, and plugins can not access the store field of neoststem as it is private, therefore this is not marked as obsolete.

Fixes # (issue)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking 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?

Test Configuration:

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[Jim8y]

This pr blocks neo-project/neo-modules#873 , will update it once this is merged.

[roman-khimov]

It'd be nice to mention #3124 where this regression came from.