Fix newly enforced package:pedantic lints (#111)

- always_declare_return_types
- annotate_overrides
- omit_local_variable_types
- prefer_conditional_assignment
- prefer_if_null_operators
- prefer_single_quotes
- use_function_type_syntax_for_parameters

Ignore prefer_collection_literals lints since they would require
incorrect code where a `{}` (statically a `Map`) is assigned to a static
`LinkedHashMap`. See https://github.com/dart-lang/linter/issues/1649

analysis_options.yaml

@@ -1,6 +1,8 @@
 include: package:pedantic/analysis_options.yaml
 analyzer:
   errors:
+    # https://github.com/dart-lang/linter/issues/1649
+    prefer_collection_literals: ignore
     unused_element: error
     unused_import: error
     unused_local_variable: error