fix: Broken tests + upgrade to Blockly 12.0.0.

[BenHenning]

Fixes #525

These tests were broken as a result of RaspberryPiFoundation/blockly#9045 and have been updated as such:

• Many of these existing getCurrentFocusNodeId calls have been updated to use a new getCurrentFocusedBlockId since they actually want to match against a block's data ID rather than its focus-specific ID (which is new as of fix: Ensure BlockSvg is uniquely focusable on the page blockly#9045).
• There are still some existing uses for getCurrentFocusNodeId (specifically fields).

Separately, clickBlock has been removed. Its uses were removed in #482 (I think) in favor of direct keyboard navigation. I suspect this is the pattern we want to keep moving forward since it has better alignment with real user behavior, so removing the helper ensures tests don't fall back on it instead of trying to use real navigation.

Finally, this PR also updates the plugin to 12.0.0 of Blockly now that it's fully launched. I've tested this against a variety of scenarios yesterday and today so it seems to be working pretty well (#526 notwithstanding). Additionally, the CI workflows have been updated to link against latest develop as the new "tip-of-tree" v12. Unfortunately there was a behavioral discrepancy between beta.7 and the full 12.0.0 release which resulted in 1 new test failing. This will be fixed by RaspberryPiFoundation/blockly#9063 but it means two things:

1. The CI for this PR won't pass until fix: Ensure FieldImage is clickable when appropriate blockly#9063 is merged.
2. The main branch's CI won't pass once this is merged due to that one test failing. Once we push a 12.0.1 or 12.1.0 version of Blockly and update this plugin accordingly, the test will start passing in main's CI.

[BenHenning]

Currently investigating 1 new failure that is somehow different between beta.7 and 12.0.0.

[BenHenning]

Ah. From testing it seems that RaspberryPiFoundation/blockly#9054 caused this new failure.

Test Right from text block selects shadow block then field is failing due to the quote image fields now becoming navigable.

[BenHenning]

I've verified that the tests are passing when linked against RaspberryPiFoundation/blockly#9063. This PR should block on being merged until its CI passes (i.e. after RaspberryPiFoundation/blockly#9063 is merged), however it can still probably be reviewed now.

[BenHenning]

Self-reviewed changes.

FYI I noticed that my regeneration of package-lock.json includes some possibly unexpected removals. While everything is running well locally, I wonder if this has something to do with my local npm version.