Variable declaration to be 'final' by default

I have observed that in my code the most variables I declare are 'final' and rarely I use some 'non final' variable declaration.

`final int id = 1;`
`id = 2 // The final variable 'id' can only be set once.`

I would propose the variables in Dart to be final by default without the keyword 'final' before the type of variable. This would save some typing.

`int id = 1;`
`id = 2 // The final variable 'id' can only be set once.`

It could be introduced the keyword 'mutable' to declare a non-final variable

`mutable int id = 1;`
`id = 2 // Accepted`

No files, tests, or entry points are named. Start by reading the issue and its discussion to determine the language-design scope; done would require a documented decision on the proposed default variable mutability and syntax.

Written by the indexing model from the issue text.