HCL - allow for expression on LHS in objectelem

[greg-at-moderne]

What's changed?

Adding the support for expressions in object elements in HCL. These are typically used for provider aliases in Terraform configuration files, e.g.

                providers = {
                  aws = aws
                  aws.dns = aws
                }

What's your motivation?

To fix parsing errors of valid Terraform code.

[timtebeek]

Great to see, thanks! I've not looked at any of the internal classes beyond the HclParserVisitor, assuming those are all generated. If I should have a closer look there feel free to call out anything with a self-review. If not, then we're ready to merge. 🚀

[greg-at-moderne]

Yep. All changes in rewrite-hcl/src/main/java/org/openrewrite/hcl/internal/grammar are generated code based on the .g4 lexer/parser.