Generate property set accessor code for org.osate.contribution.sei

[AaronGreenhouse]

Summary

The property set accessor code the property sets provided by org.osate.contribution.sei should be generated (using the tool in org.osate.propertiescodegen and put into this project.

[AaronGreenhouse]

See https://github.com/osate/osate2/wiki/Properties-Code-Generator

[AaronGreenhouse]

• Added generated code to org.osate.contribution.sei in a new src-gen directory.
• Added @codegen-package tags to the property set definitions
• Deprecated the classes in org.osate.contribution.sei.names
• Deprecated the class GetProperties in project org.osate.xtext.aadl2.properties
• Removed the the dependency on org.osate.contribution.sei from org.osate.xtext.aadl2.properties

[lwrage]

Please add "Will be removed in 2.10.0" to the @deprecated javadoc tag so people know what to expect.