Consider strings validation for getUniformIndices and getUniformBlockIndex

_Another follow-up to https://github.com/KhronosGroup/WebGL/issues/3727._

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

Read the WebGL 2.0 specification entries for getUniformIndices and getUniformBlockIndex, then compare validation of uniformNames and uniformBlockName with the name parameter rules for getAttribLocation and getUniformLocation. Done means the specification consistently defines maximum lengths and allowed characters for these parameters.

Written by the indexing model from the issue text.