* Warn when Items key isn't directly accessible
Go template requires that map keys are alphanumeric for direct access
using the dotted reference syntax. This warns users when they create
keys that run afoul of this requirement.
- cli: use regex to detect invalid indentifiers in var keys
- test: fix slash in escape test case
- api: share warning formatting function between API and CLI
- ui: warn if var key has characters other than _, letter, or number
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Co-authored-by: Charlie Voiselle <464492+angrycub@users.noreply.github.com>
Co-authored-by: Luiz Aoqui <luiz@hashicorp.com>
