(core) Add rules to eslint to better match our coding conventions.

Summary:
We used tslint earlier, and on switching to eslint, some rules were not
transfered. This moves more rules over, for consistent conventions or helpful
warnings.

- Name private members with a leading underscore.
- Prefer interface over a type alias.
- Use consistent spacing around ':' in type annotations.
- Use consistent spacing around braces of code blocks.
- Use semicolons consistently at the ends of statements.
- Use braces around even one-liner blocks, like conditionals and loops.
- Warn about shadowed variables.

Test Plan: Fixed all new warnings. Should be no behavior changes in code.

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D2831

app/client/aclui/AccessRules.ts

@@ -1067,7 +1067,7 @@ class ObsUserAttributeRule extends Disposable {
                     // TODO this weirdly only works on the first click
                     (editor as any).completer?.showPopup(editor);
                   }
-                })
+                });
               })
             }),
             testId('rule-userattr-attr'),