blocklyStackGlowFilter does not have a unique id

[rachel-fenichel]

https://github.com/LLK/scratch-blocks/blob/develop/core/inject.js#L118 states that

// Each filter/pattern needs a unique ID for the case of multiple Blockly
// instances on a page. Browser behaviour becomes undefined otherwise.
// https://neil.fraser.name/news/2015/11/01/
// TODO (tmickel): Look into whether block highlighting still works.

but the stack glow filter and replacement glow filter do not follow this rule.