Add explicit field IDs to flatbuffer schemas

[jameskuszmaul-brt]

Changelog

Added explicit field IDs to flatbuffer schemas.

Docs

None

Description

This allows the schemas to be compiled with --require-explicit-ids turned on in flatc, which can be nice to help prevent people from accidentally making breaking changes to flatbuffer schemas if they choose to reorder fields (or insert new fields in the middle of the schemas). Because of how flatc works with includes, if downstream users want to use --require-explicit-ids on their own schemas that happen to include foxglove schema types, they must update the foxglove schemas that they use to include IDs.

[jameskuszmaul-brt]

Waiting on #147 for CI....

[jtbandes]

Something worth noting is that we have a mechanism here for specifying field ids explicitly for protobuf (protobufFieldNumber). This was added in #61 because we wanted to add a field, but put it in a different order in the IDL, without changing the ids of existing fields.

This isn't currently an issue for flatbuffers because we created these .fbs files after making that change (#70) and these ids you've added should correspond with the existing field order today. But anyway, since the Foxglove app uses the binary schemas from the MCAP file, this probably won't matter for our purposes — only for external users who are associating this schema with some pre-existing data.

...and actually, while writing this comment I discovered we added a new field in a different order in #108 after the .fbs files were first published (cc @defunctzombie). It was probably a miss that we didn't do this field numbering thing back then. (Amusingly, we discussed the issue in #108 (comment) for protobuf but forgot about flatbuffers.) Anyway, what's done is done :)