Update to ListView Sample Code in API Docs (#29072)
Update to ListView Sample Code in API Docs (#29072)

* Updated ListView Sample code with more examples for different constructors and also to match asset diagrams.

* Fixed MIA semicolons.

* Code cleanup.

* Added context for ListView.builder example.

* Analyzer does not like const and static usages.

* Replaced the const declarations with final. The analyzer does not like the use of const here, at all.

* Fixed parameterized declarations.

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