Small bug fix: Correctly incorporate column offset in decorations

[patrys]

This fixes the case where error markers are placed incorrectly when an error refers to a range in the first line of inlined GraphQL.

Previously error locations (and thus editor decorations) would disregard the column offset. Error were reported like this:

foo = gql`query Foo { bar }`
            ^^^

This change makes the location add the column offset it referring to the first line:

foo = gql`query Foo { bar }`
                      ^^^

[apollo-cla]

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[martijnwalraven]

Thanks a lot for tracking this down and fixing it, tests are especially appreciated!