Allow definition of targets in kebab-case but access via camelCase

For attributes, I define in the markup `data-my-attr-name` and in the controller as `@attr myAttrName`

For targets however, I have to define the target name in both the markup and the controller using camelCase:
`data-targets="my-controller.myTargetsName"` and `@targets myTargetsName`
I think it would be nice (more consistent?) if the markup could support kebab-case.

Start by locating the target-name handling and the existing attribute conversion behavior. Compare the markup examples for kebab-case and camelCase, then add coverage showing that a kebab-case target can be accessed through the camelCase controller property; done means both forms work consistently.

Written by the indexing model from the issue text.