Generate type aliases in Dart

[DanielKamkha]

Added dedicated DartTypeAlias template, as type aliases (typedefs) are now supported in Dart language (since Dart version 2.13). Updated other Dart tempates and resolvers to treat type aliases as a normal type, instead of skipping it through to the target type.

Added/updated related smoke and functional tests.

Unrelated smoke tests are updated in a separate commit.

Resolves: #907 Signed-off-by: Daniel Kamkha [email protected]