One Scenario File to cover all basic features of TypeSpec

[lirenhe]

Currently, we use different typespec 'scenarios' files to verify the codegen capability for different features.
With the recent work to reduce the number of generated files merged into the repos, we need to have one Scenario File to cover all basic features of TypeSpec.

Please note:

1. The generated SDK code for this spec will be committed into the TypeSpec repo.
2. This test case will be focus on the board instead of depth coverage, so there is no need to add side cases.

[timotheeguerin]

this feels like a nightmare to maintain and is just not possible anyway as many features are service level features that need a whole spec.