fix(plugin): export read-only table fields to the plugin API

[gnosek]

What type of PR is this?

Uncomment one (or more) /kind <> lines:

/kind bug

/kind cleanup

/kind design

/kind documentation

/kind failing-test

/kind feature

Any specific area of the project related to this PR?

Uncomment one (or more) /area <> lines:

/area build

/area ci

/area event

/area event_derive

/area plugin

/area plugin_api

/area plugin_derive

/area plugin_tests

What this PR does / why we need it:

ReadOnly<T> fields were never exported to the plugin API, effectively making them private.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

[Andreagit97]

/approve

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Andreagit97, gnosek

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[poiana]

LGTM label has been added.

Git tree hash: 7cee52a7773cf4991e911c030616516b43e4e269