Add extra keys rejection to `Scarb.toml` parsing

[FroyaTheHen]

The extra/mismatched (same thing) keys should not be accepted and treated as an error

[piotmag769]

Wdym by "do not accept"? Imo they should be accepted, but emit a warning diagnostic. I am assuming we are talking about LS diagnostics only, right (not ones generated during scarb build etc.)?

[FroyaTheHen]

@piotmag769, it's understandable you find it unclear and misleading. Please, hear me out!
The need for implementing diagnostics for manifest came up during discussion over (ls) hover for Scarb.toml. As it is valid yet out of scope I did create the separate task. The choice of wording presents the idea and neither attempts to explore the depth of the task nor suggest the implementation. Please, treat it more as a one-phraser description. It can and should be extended by whoever takes the task. Ofc, feel free to comment with suggestions or even edit the task itself. 🙏