Update dependency to use analyzer 13

[eernstg]

This PR changes the dependencies in the reflectable packages to use analyzer ^13.0.0 and migrates the code generator accordingly. In particular:

Analyzer ^13.0.0 removes the class DefaultFormalParameter. Default values are now handled via a property on FormalParameter. Old approach: Check if a parameter node is a DefaultFormalParameter, access its defaultValue. New approach: Check the defaultClause property on a FormalParameter or RegularFormalParameter and access its value.

Similarly, the class NamedExpression has been removed and replaced by NamedArgument, in order to model named arguments in an ArgumentList. Old approach: Use expression is NamedExpression and access expression.name and expression.expression. New approach: Use expression is NamedArgument and access expression.name.lexeme to get the label name and expression.argumentExpression to get the value.

Finally, the arguments property of ArgumentList now returns a NodeList<Argument> instead of a NodeList<Expression>. Various loops have been updated to use the new types.

This PR also prepares reflectable for a release as v5.2.3 and reflectable_builder as v1.2.3. Version v5.2.3 of reflectable doesn't actually change anything other than the version, but I'd like to allow all usages of reflectable and reflectable_builder to remain in sync with respect to the version number such that developers can always update those two IDs together (e.g., from 5.2.2 to 5.2.3 along with 1.2.2 to 1.2.3, simultaneously).

Finally, this PR fixes a bug in 'example.dart' (where a lint asked for a type annotation on a parameter, but the type annotation which was added was wrong).

[eernstg]

Hello @sigurdm, the update to analyzer 12.0.0 turned out to be non-breaking (as seen from this package, at least), so I took another step and updated it directly to analyzer 13.0.0.