Better error message in declarations of final and const variables without a value

[jjosenaldo]

In commands like final x;, const x;, final int x; and const int x;, the error message showed is The final variable ';' must be initialized. It would be better if it was The final variable 'x' must be initialized instead.

[lrhn]

Looks like an off-by-one bug in the front-end. Reproduces on dartpad for local variables.