x/website: update to latest spec just before release

[griesemer]

To get the most up-to-date spec into the 1.18 release, rather than cherry-picking possibly multiple CLs until the release, we should create a single CL (immediately before the release) in the release branch which contains a 1:1 copy of the latest spec at tip.

cc: @dmitshur

[gopherbot]

Change https://go.dev/cl/392674 mentions this issue: [release-branch.go1.18] doc: update go_spec.html with latest changes

[gopherbot]

Closed by merging 428533f to release-branch.go1.18.

[zigo101]

Just found there a dup is in spec. Just search is is.

[griesemer]

@go101 I will take care of this for the next version. Thanks.

[zigo101]

Some inconsistencies between spec and gc:

• a call to the close function doesn't require its argument has a core type, but spec says it requires.
• for a neither a map nor a type parameter container, index expression is not required to have a core type, but the spec says it is required (I have mentioned this several times and still think it is not right described in the spec)