fix(query): correcly escape LogicalPlan-to-String backslashes

[alextheimer]

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• [x] The commit(s) message(s) follows the contribution guidelines ?
• [x] Tests for the changes have been added (for bug fixes / features) ?
• [ ] Docs have been added / updated (for bug fixes / features) ?

Currently, escape characters themselves may not be correctly escaped when LogicalPlans are converted to Strings. This may cause e.g. parse errors when plans are converted to Strings then sent remotely. This PR adds the correct escape characters to all miscellaneous function args; these may contain regex and require backslash escapes.