add support for ".resource" files

[ghost]

Robot framework 3.1 added the option to use .resource extension for resource files instead of .robot

https://robotframework.org/robotframework/latest/RobotFrameworkUserGuide.html#resource-files

[ghost]

As a work-around, it is possible to manually specify .resource files to be Robot Feature file types from the menu File -> Associate With File Type...

Then syntax highlight will work and keywords will be found.