add urldecode function

[ctjhoa]

This function does the inverse transformation as
urlencode.

[hashicorp-cla]

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[crw]

Thank you for submitting this PR so long ago! I am going back through older PRs and came across this one, and thought I would share the following information.

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Terraform version 1.8 launched with support of provider-defined functions. It is now possible to implement your own functions! We would love to see this implemented as a provider-defined function.

Please see the provider-defined functions documentation to learn how to implement functions in your providers. If you are new to provider development, learn how to create a new provider with the Terraform Plugin Framework. If you have any questions, please visit the Terraform Plugin Development category in our official forum.

We hope this feature unblocks future function development and provides more flexibility for the Terraform community. Thank you for your continued support of Terraform!

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I believe this may not have been reviewed for the same reason as many other functions, that the maintainer team generally does not want to add more functions to Terraform that aren't extremely general. Given the age, I am going to close this PR. If you would like me to re-open it for consideration, please let me know and also agree to the CLA (see the comment above). Thanks!