(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/common/ActionSummary.ts

@@ -240,7 +240,7 @@ export function getAffectedTables(summary: ActionSummary): string[] {
  */
 export function getTableIdBefore(renames: LabelDelta[], tableIdAfter: string|null): string|null {
   if (tableIdAfter === null) { return tableIdAfter; }
-  const rename = renames.find(rename => rename[1] === tableIdAfter);
+  const rename = renames.find(_rename => _rename[1] === tableIdAfter);
   return rename ? rename[0] : tableIdAfter;
 }
 
@@ -250,7 +250,7 @@ export function getTableIdBefore(renames: LabelDelta[], tableIdAfter: string|nul
  */
 export function getTableIdAfter(renames: LabelDelta[], tableIdBefore: string|null): string|null {
   if (tableIdBefore === null) { return tableIdBefore; }
-  const rename = renames.find(rename => rename[0] === tableIdBefore);
+  const rename = renames.find(_rename => _rename[0] === tableIdBefore);
   const tableIdAfter = rename ? rename[1] : tableIdBefore;
   if (tableIdAfter?.startsWith('-')) { return null; }
   return tableIdAfter;