iCalendar import: merge RDATE/EXDATE into recurrence overrides #89
Description
Context
Per draft-ietf-calext-jscalendar-icalendar-22, RDATE and EXDATE properties should be represented as entries in recurrenceOverrides:
- RDATE values become keys in
recurrenceOverrideswith an empty PatchObject (indicating the occurrence exists with no property changes) - EXDATE values become keys in
recurrenceOverrideswith{ "excluded": true }
This is how JSCalendar unifies the three iCalendar recurrence-modification mechanisms (RDATE, EXDATE, RECURRENCE-ID overrides) into a single recurrenceOverrides map.
Current behaviour
RDATE and EXDATE are preserved as flat lists (rdates and exdates fields) on the entry record. This is a direct transliteration of the iCalendar structure rather than a semantic translation.
Expected behaviour
RDATE and EXDATE values should be merged into a recurrence_overrides map alongside any RECURRENCE-ID overrides (see #RECURRENCE-ID issue). This may depend on or be done together with the RECURRENCE-ID grouping work.