Backport of update hcl@v2.11.0 into v1.1

[teamterraform]

Backport

This PR is auto-generated from #30056 to be assessed for backporting due to the inclusion of the label 1.1-backport.

The below text is copied from the body of the original PR.

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v2.11.0 (Dec 1, 2021)

Enhancements

• hclsyntax: Various error messages related to unexpectedly reaching end of file while parsing a delimited subtree will now return specialized messages describing the opening tokens as "unclosed", instead of returning a generic diagnostic that just happens to refer to the empty source range at the end of the file. This gives better feedback when error messages are being presented alongside a source code snippet, as is common in HCL-based applications, because it shows which innermost container the parser was working on when it encountered the error. (#492)

Bugs Fixed

• hclsyntax: Upgrading an unknown single value to a list using a splat expression must return unknown (#493)

Fixes #29973

[github-actions]

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