Use `NcSelect` instead of `NcMultiselect` in the components

[raimund-schluessler]

Since NcMultiselect got deprecated, we should stop using it in the components itself and use NcSelect instead.

Means, we need to migrate here:

• NcActionInput Use NcSelect for NcActionInput type multiselect #3760
• NcTimezonePicker Use NcSelect for NcTimezonePicker #3781
• NcSettingsSelectGroup Improve NcSettingsSelectGroup - Convert to NcSelect #4120
  https://github.com/nextcloud/nextcloud-vue/blob/4ac3029b10dc54f68a451f3496bbf6bef5272a37/src/components/NcSettingsSelectGroup/NcSettingsSelectGroup.vue#L25-L41
• NcSearch Use NcSelect in NcRichtext #4247
  https://github.com/nextcloud/nextcloud-vue/blob/026afe9a4c8959be853cccbef825fe7b6da8398e/src/components/NcRichText/NcReferencePicker/NcSearch.vue#L3-L10
• NcProviderList Use NcSelect in NcRichtext #4247
  https://github.com/nextcloud/nextcloud-vue/blob/026afe9a4c8959be853cccbef825fe7b6da8398e/src/components/NcRichText/NcReferencePicker/NcProviderList.vue#L3-L8

@Pytal @susnux Just for reference.

[Pytal]

master currently targets v7 major, so this breaking change will have to be done for v8

[raimund-schluessler]

master currently targets v7 major, so this breaking change will have to be done for v8

I think it doesn't have to be a breaking change if we do it right.

[Pytal]

I think it doesn't have to be a breaking change if we do it right.

Could review a non-breaking PR if you'd be so inclined then :)