Validate Entity names match allowed REGEX (client side)

Includes all parts of the namespace for all entities (e.g., Actions, Triggers, Rules, Packages, etc.)

Regex used at server-side is:
protected[core] val REGEX = raw"\A([\w]|[\w][\w@ .-]{0,${ENTITY_NAME_MAX_LENGTH - 2}}[\w@.-])\z"
private val entityNamePattern = REGEX.r.pattern // compile once

where: ENTITY_NAME_MAX_LENGTH=256