Check if a variable name might need a prefix.

Prefix is not needed for:
- superglobals,
- WP native globals,
- variables which are already prefixed.

@since 0.12.0
@since 1.0.1  Added $stackPtr parameter.

@param int    $stackPtr The position of the token to record the metric against.
@param string $name     Variable name without the dollar sign.

@return bool True if the variable name is whitelisted or already prefixed.
False otherwise.