Add is_* getters to check candidate type without using the string constants directly. Bug: none Change-Id: I82c83c032a30a1c67de2d5d6168ecc04e0254318 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/334800 Reviewed-by: Harald Alvestrand <hta@webrtc.org> Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org> Cr-Commit-Position: refs/heads/main@{#41568}