Block editors - replaces hardcoded -20 with current node ID

[leekelleher]

Prerequisites

• I have added steps to test this contribution in the description below

Description

When a Block editor makes a call to contentResource.getScaffoldByKeys() (to get the element type schemas), it currently passed through a hardcoded ID of -20. This patch replaces the hardcoded ID with the current page/node's ID, with a fallback on parent page/node, (and a final fallback on the previous hardcoded ID -20.

The motivation behind this pull request is that with my Contentment package's Data List editor has a feature to make use of the current page/node, but it can only do this when the id or parentId parameters are available in the GetEmptyByKeys() content API request. This works fine within page-level property-editors, but it doesn't work with the BlockList/BlockGrid editors, (this issue also applies to NestedContent, but since that is deprecated, I didn't look to patch that too).
I regularly have support requests for Contentment to support Block editors better.

Steps to test
View a content page/node with either the BlockList or BlockGrid editors configured, and verify that it still works as expected.

In theory, this shouldn't be a breaking-change, but in reality, there may be a scenario where a developer is relying on the -20 ID being present, and would break their implementation. Personally, I can't see why someone would do this, but I submit to much wiser developers than me. 🤗

[github-actions]

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[sniffdk]

Thanks for this PR @leekelleher, we've (me and some colleagues) been hit by this problem just this week and are happy to see you have a fix implemented 🙏

[nul800sebastiaan]

Thanks for this one @leekelleher - works well and I honestly can't see it breaking anything either!

[leekelleher]

Super, thank you @nul800sebastiaan! 🙏

[ljfio]

@nul800sebastiaan Is there a chance this fix could be back ported to v10? We're hitting this very problem with our build!