Bump @typespec/compiler from 1.3.0 to 1.4.0 in /additions

Bumps [@typespec/compiler](https://github.com/microsoft/typespec) from 1.3.0 to 1.4.0.
- [Release notes](https://github.com/microsoft/typespec/releases)
- [Commits](https://github.com/microsoft/typespec/compare/typespec-stable@1.3.0...typespec-stable@1.4.0)

---
updated-dependencies:
- dependency-name: "@typespec/compiler"
  dependency-version: 1.4.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]