(experiment) feat(gems): gems goes multivat

[kumavis]

highlight: durable lazy presences for remote objects via ExtRefController that can lazily trigger their underlying captp connection upon use

requires captp external table support: https://github.com/endojs/endo/pull/2564

see relevant test: https://github.com/endojs/endo/blob/f1ea4a3a25b6363b3505037f51d7b3e717893735/packages/gems/test/extref.test.js#L22-L32