fix(spy)!: spyOn reuses mock if method is already spyed on

[sheremet-va]

Description

Fixes #6419
Fixes #6465

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[sheremet-va]

@hi-ogawa need heelp

[hi-ogawa]

I don't think we need to change automocker since class instance's const original = this[key] is not an owned property, so spyOn can ignore it and add the new spy as owned prop.
This means that reusing spyOn only happens for owned prop, but that behavior is probably reasonable.