* chore: fix uses of var in core/block_dragger
* chore: fix uses of var in core/extensions.js
* chore: fix uses of var in core/field_multilineinput.js
* chore: fix uses of var in assorted core files
* chore: fix uses of var in node test runner and playground screenshot code
* fix: undefined return from measureFontMetrics
* fix: violations of no-const-assign
* chore: only one variable declaration per line
Our files are up to a decade old, and have churned so much, that the initial author of the file no longer has much meaning.
Furthermore, this will encourage developers to post to the developer group, rather than emailing Googlers (usually me) directly.
