Enforce line and column indices for all language modules

[tsaglam]

Remove the possibility to use the singular index in frontends, thus enforcing line and column indices for all language modules. Currently, all language modules support this, and new ones will be required to do so. For more information see this comment. Detailed changes:

• Remove Language#supportsColumns() (as we now assume this is always true)
• Remove Token.getIndex() as this is now no longer needed
• Adapt the ComparisonReportMapper accordingly

(currently a draft PR as this can be merged AFTER the upcoming PISE PRs)

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