Plan renderer: Support users indexing integer paths with stringified numbers

[liamcervante]

Terraform allows users to specify indexes as strings as long as the string can be converted into a number. For example, the following are equivalent:

• test_resource.resource.list[0].attribute
• test_resource.resource.list["0"].attribute
• test_resource.resource.list["0.0"].attribute

While the following would all raise validation errors.

• test_resource.resource.list[0.5].attribute
• test_resource.resource.list["not a number"].attribute
• test_resource.resource.list["0.5"].attribute

The plan renderer currently makes an assumption that the indices will be the appropriate type. This causes a panic when attributes like those listed above are included in the relevant attributes data, as the renderer will attempt to cast them into the wrong type.

This PR updates the logic for parsing paths within the renderer so that it will attempt to convert strings into integers and panic if it can't. The panic should be okay and never triggered as Terraform will fail earlier if the index is actually invalid.

Fixes #33472

Target Release

1.5.3

Draft CHANGELOG entry

BUG FIXES

• Fixes crash when rendering the plan if a relevant attribute contains an integer index specified as a string.

[kmoe]

+1.5-backport

[github-actions]

Reminder for the merging maintainer: if this is a user-visible change, please update the changelog on the appropriate release branch.

[github-actions]

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