docs: apply final review suggestions to dot shorthands guide

[lamek]

Adds a guide on Dart shorthands to the flutter docs.

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Clone of #13180. Ran into some Git issues locally.

[gemini-code-assist]

Code Review

This pull request updates the documentation for Dart dot shorthands by refining the explanation of context types and simplifying the code examples. A grammatical error was identified in the section regarding enums where 'is expects' should be corrected to 'expects'.

[gemini-code-assist]

The phrase "is expects" is grammatically incorrect. It should be "expects" or "is an".

Suggested change

	When the context type is expects an `enum`, such as `mainAxisAlignment`, you can omit the
	When the context type expects an enum, such as mainAxisAlignment, you can omit the