[ENHANCEMENT] Add validation and auto-completion for keys in a DotDict

[mardukbp]

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

Robot Framework has its own dictionary class DotDict, that allows retrieving a value from a (nested) dictionary using dot syntax. For example, ${dict.some_key}. Robot Code validates whether the variable ${dict} is defined, but it does not validate whether the key some_key is defined.

Describe the solution you'd like

Robot Code should validate whether a key exists in a Robot Framework dictionary (DotDict) and provide feedback when a key is not defined. Knowing which keys are defined would allow implementing auto-completion for them.

Describe alternatives you've considered

N/A

Additional context

N/A