feat(captp): allow external import/export tables

[kumavis]

This PR exposes an optional configuration for captp that allows you to:

• manage the import/export tables
• construct the presences for imported remote values
• specify slots for exported values

This may be useful If you want:

• make import/export tables persist across captp "sessions" (make the references non-brittle to network issues)
• to customize captp remote presences (eg make them lazily initiate captp connections when used)

This change was motivated by working on the ExternalReferenceController of the gems experiment, which enabled durable imported presences with lazy captp connections re-established on use.

This is an alternate implementation of https://github.com/endojs/endo/pull/2562, which ended up duplicating import/export tables inside and above captp.

ExtRefController migration notes from alternative implementation:

• passing in import/export tables
  • replaces opts.gcHook (export table)
  • replaces opts.missingExportHook (export table)
  • replaces captp.exportValue (export table)
  • replaces captp.importSlot (import table)
• providing a slot provider
  • replaces opts.onBeforeExportHook (retrieving slot)
• providing a presence creator
  • replaces opts.onBeforeExportHook (creating a presence)
• still need captp.makeRemoteKit

[kumavis]

is something missing from the tables? traps? gcImports in MakeCapTPImportExportTablesOptions seems lonely -- maybe pass in all options?