Consider name validation for getFragDataLocation

_A follow-up to #3727._

The current WebGL 2.0 specs do not apply the same string validation rules (max length and allowed characters) to the `name` parameter of the `getFragDataLocation` command as to the `name` parameter of `getAttribLocation` or `getUniformLocation`. This is likely an oversight.

No repository files or tests are named in the issue. Start by reading the WebGL 2.0 rules for getFragDataLocation alongside getAttribLocation and getUniformLocation, and review follow-up issue #3727; completion criteria are not specified beyond deciding whether matching name validation should apply.

Written by the indexing model from the issue text.