Support --experimental_allow_proto3_optional option

[2is10]

Is your feature request related to a problem? Please describe.

Since protoc version 3.12.0, --experimental_allow_proto3_optional enables the use of optional in proto3 for explicit field presence.

https://github.com/protocolbuffers/protobuf/blob/master/docs/field_presence.md

When I try to use --experimental_allow_proto3_optional, it’s unrecognized in IntelliJ, and the optional keyword is still forbidden.

Describe the solution you'd like

See screenshots. Ideally there would be no errors.

Additional context

[jvolkman]

This plugin isn't supported anymore. Maybe add a note to https://github.com/jvolkman/intellij-protobuf-editor/issues/7?

[kshchepanovskyi]

This issue is closed as plugin is not supported anymore. Please switch to https://github.com/jvolkman/intellij-protobuf-editor.