Point references to the Web IDL spec to its new URL.

The Web IDL spec was moved from https://heycam.github.io/webidl to
https://webidl.spec.whatwg.org (the anchors continue to work). Update
all references to the old URL.

While here, also make sure all links use https rather than http.

Change-Id: I95370a9ddafbbb2dc34ccf3bc96b3dc7dd747d61
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3229371
Auto-Submit: Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>
Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/main@{#932492}