(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/components/ActionLog.ts

@@ -440,7 +440,7 @@ export class ActionLog extends dispose.Disposable implements IDomComponent {
     const fieldIndex = viewSection.viewFields().peek().findIndex((f: any) => f.colId.peek() === colId);
 
     // Finally, move cursor position to the section, column (if we found it), and row.
-    this._gristDoc.moveToCursorPos({rowId, sectionId, fieldIndex}).catch(() => { /* do nothing */});
+    this._gristDoc.moveToCursorPos({rowId, sectionId, fieldIndex}).catch(() => { /* do nothing */ });
   }
 
 }