Extract rule: template-no-bare-strings

[NullVoxPopuli]

Split from #2371.

[johanrd]

Claude Review: comparing against ember-template-lint no-bare-strings

<Input>/<Textarea> handling differs from original. The original skips BUILTIN_COMPONENT_ATTRIBUTES (Input/Textarea placeholder/@placeholder) in strict mode (gjs/gts) because these names could
refer to custom components named Input and Textarea, not Ember built-ins — preferring false negatives over false positives. The PR always checks them regardless of mode.

This is the only behavioral difference I found. Everything else matches: allowlist (all 67 entries), globalAttributes/elementAttributes defaults, page-title/if/unless/concat helper handling, config
merging for object and array forms, ignored elements, and the GJS <template> wrapper detection.