[Feature]: Remove Preview. prefix from function calls and use preview as a property in settings

[v-raghulraja]

Is your feature request related to a problem? Please describe.

Currently, PowerFx test steps use the Preview. prefix in function calls (e.g., Preview.AssertJavaScript).
We want to refactor this so that the Preview. prefix is removed from all function calls in test steps, and instead, a preview property is used in the test settings/configuration.
The preview context should be determined by this property, not by the function name.

Describe the solution you'd like

Currently, PowerFx test steps use the Preview. prefix in function calls (e.g., Preview.AssertJavaScript).
We want to refactor this so that the Preview. prefix is removed from all function calls in test steps, and instead, a preview property is used in the test settings/configuration.
The preview context should be determined by this property, not by the function name.

Describe alternatives you've considered

No response

Additional context?

No response