New rule: Report un-resolvable import expressions

[FloEdelmann]

I'd like to suggest a rule that reports # import expressions which point to a non-existing file:

Fail

# import Foo from 'nonExistingFile.graphql'
#                 ^^^^^^^^^^^^^^^^^^^^^^^^^ File 'nonExistingFile.graphql' does not exist.

query MyQuery {
  bar
}

# import 'nonExistingFile.graphql'
#        ^^^^^^^^^^^^^^^^^^^^^^^^^ File 'nonExistingFile.graphql' does not exist.

query MyQuery {
  bar
}

Pass

# import Foo from 'existingFile.graphql'

query MyQuery {
  bar
}

[dimaMachina]

Accepted