Blockly v10.4.0

This release contains mostly bug fixes and improvements!
New feature: custom connection previewers allow you to change how pending connections are visualized to users. Check out the documentation to learn more.
Note if you use TypeScript: we now export the JavascriptGenerator (and similiar for other languages) class in TypeScript, complete with its accurate typings. We were not previously exporting this class in our TS definition files, so it wasn't accessible from TS code at all. Do note that we are still exporting the instance of those classes (javascriptGenerator and friends) typed as any so as not to introduce breaking type changes. You'll get accurate typings for the instances as well coming in v11!

What's Changed

fix: Remove double spaces in translation instructions. by @NeilFraser in #7704
fix: updated mocha tests to display error messages by @btw17 in #7706
fix: prevent flyout block highlighting during workspace drag by @neerajkumarc in #7720
fix: prevent console logging duplicate deprecation warnings by @ebrahim95 in #7733
fix: triggering flyout show from field render causing infinite loop by @BeksOmega in #7784
fix: cancelling all renders on triggering queued renders by @BeksOmega in #7787
fix: first block dragged from flyout will have same id by @maribethb in #7788
fix: prevent block change event firing if editing is cancelled by using keypress by @ebrahim95 in #7794
fix: shadow blocks with variable fields are allowed to be deserialized from XML by @ebrahim95 in #7802
fix: manually add typings for generator classes by @maribethb in #7824
fix: destroy connection highlight when the connection is disposed by @BeksOmega in #7830
fix: fix reference docs toc generation by @maribethb in #7832
fix: insertion marker previewer finding wrong connection for different conn counts by @BeksOmega in #7833
fix: disposing of connection previewer by @BeksOmega in #7834

Full Changelog: blockly-v10.3.1...blockly-v10.4.0