Thanks for your comments. Here is my response to each one.
1. I have added the license to each newly created file.
2. Although i have copied GroovyParticipantExtensionPoint code, but i have made some changes which make sense for groovy refatcoring. However i have included the original license with the file
3. GroovyParticipantExtensionPoint uses the existing extension point exposed by eclipse ltk, that's why i have not included any exsd file with it.
4. I cannot pass IJavaElement to RenameMethodProvidor because i need to get a handle on SourceMethod selected by the user, for this purpose i need handle to editor, if i try to get a handle to selected method node within GroovyRenameAction then it gives me an empty text selection, getGroovyCompilationUnit() only gives handle to ITypeRoot but not to the SourceMethod selected by the user for rename, please let me know if you can think of some other workaround for this.
I have attached a new patch here