Scatter plot: formula lines cannot be edited in some cases

[katerina-stepanova]

v1.22.2

Steps to reproduce:

1. Add a scatter plot
2. Open formula lines dialog and add a line
3. Edit formula: move the 2nd column from the right side of equation to the left side of equation
   E.g. if it was ${Chemical Space Y} = ${Chemical Space X} + 1, change it to ${Chemical Space Y} - ${Chemical Space X} = 1
   Note: at this step the line itself disappears and formula is underlined with thin red line:

4. Click OK
5. Open formula lines dialog again

Expected results:

1. Previously added formula line should be editable, even if invalid. Preview should show relevant columns.
2. Indication of invalid lines should be more clear, ideally it should not be possible to save an invalid configuration.
3. In this particular case, ${Chemical Space Y} = ${Chemical Space X} + 1 and ${Chemical Space Y} - ${Chemical Space X} = 1 are equivalent, both should be supported.

Actual results: Previously added formula line cannot be edited: right side of the dialog is blank on clicking the line. Also, preview is showing wrong columns.

Error:

logger.ts:108 
 end of input expected at 1:43
	packages/$sdk/lib/_internal/js_runtime/lib/js_helper.dart 1772:17  wrapException
	packages/$sdk/lib/_internal/js_runtime/lib/js_helper.dart 1807:25  throwExpression
	packages/petitparser/src/core/contexts/failure.dart 14:13          Failure.value
	packages/d4/src/viewer_base/formula_lines_mixin.dart 89:16         FormulaLineHelper._parseLineFormula
	packages/d4/src/viewer_base/formula_lines_mixin.dart 71:7          FormulaLineHelper.setup
	packages/d4/src/viewer_base/formula_lines_mixin.dart 206:5         FormulaLineHelper.getMeta
	packages/$sdk/lib/_internal/js_runtime/lib/js_helper.dart 1516:16  Primitives.applyFunctionWithPositionalArguments
	packages/$sdk/lib/_internal/js_runtime/lib/js_helper.dart 1489:11  Primitives.applyFunction
	packages/$sdk/lib/js/dart2js/js_dart2js.dart 667:13                _convertDartFunctionFast
	webpack://datagrok-api/src/helpers.ts 101:72                       FormulaLinesHelper.getMeta
	webpack://powerpack/src/dialogs/formula-lines.ts 456:46            getMeta
	webpack://powerpack/src/dialogs/formula-lines.ts 445:26            _createForm
	webpack://powerpack/src/dialogs/formula-lines.ts 996:21            update
	webpack://powerpack/src/dialogs/formula-lines.ts 196:63            _onItemChangedAction
	login.html.js?15582 62:91                                          a.__tryOrUnsub
	login.html.js?15582 60:384                                         a.next
	login.html.js?15582 58:497                                         a._next
	login.html.js?15582 58:168                                         a.next
	login.html.js?15582 39:23                                          d
	webpack://datagrok-api/src/events.ts 39:11                         <fn>
	packages/$sdk/lib/async/zone.dart 1307:16                          _RootZone.runUnaryGuarded
	packages/$sdk/lib/async/stream_impl.dart 330:5                     _BufferingStreamSubscription._sendData
	packages/$sdk/lib/async/stream_impl.dart 257:7                     _BufferingStreamSubscription._add
	packages/$sdk/lib/async/broadcast_stream_controller.dart 387:7     _SyncBroadcastStreamController._sendData.<anonymous function>
	packages/$sdk/lib/async/broadcast_stream_controller.dart 328:9     _BroadcastStreamController._forEachListener
	packages/$sdk/lib/async/broadcast_stream_controller.dart 386:5     _SyncBroadcastStreamController._sendData
	packages/$sdk/lib/async/broadcast_stream_controller.dart 254:5     _BroadcastStreamController.add
	packages/ddt/src/events/event_bus.dart 77:7                        EventBus.fire
	packages/xamgle/src/interop/grok_api.dart 649:64                   _initJsApi.<anonymous function>
	packages/$sdk/lib/_internal/js_runtime/lib/js_helper.dart 1521:16  Primitives.applyFunctionWithPositionalArguments
	packages/$sdk/lib/_internal/js_runtime/lib/js_helper.dart 1489:11  Primitives.applyFunction
	packages/$sdk/lib/js/dart2js/js_dart2js.dart 667:13                _convertDartFunctionFast
	webpack://datagrok-api/src/dataframe.ts 333:32                     set currentRowIdx
	webpack://powerpack/src/dialogs/formula-lines.ts 129:56            currentRowIdx
	webpack://powerpack/src/dialogs/formula-lines.ts 215:12            _currentItemIdx
	webpack://powerpack/src/dialogs/formula-lines.ts 210:31            setFirstItemAsCurrent

[dnillovna]

This issue has been mirrored in Jira: https://reddata.atlassian.net/browse/GROK-17282