idl-version warnings

> This isn't a priority or anything, but in the future it would be nice to parse the `idl_version` as a semver value and make sure it satisfies the semver requirement of `^1.0.0` (or whatever the supported version is at the time). And just crash otherwise with `IDL version {idl_version} not supported.`

Start by locating where the generated code or input IDL currently handles `idl_version`; the issue does not name a file or test. Add semver validation against the supported `^1.0.0` requirement and verify that unsupported versions produce the specified error.

索引モデルが issue の本文から書いたものです。