(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/ACLPermissions.ts

@@ -171,7 +171,7 @@ export function summarizePermissionSet(pset: PartialPermissionSet): MixedPermiss
   for (const key of Object.keys(pset) as Array<keyof PartialPermissionSet>) {
     const pWithSome = pset[key];
     // "Some" postfix is not significant for summarization.
-    const p = pWithSome === 'allowSome' ? 'allow' : (pWithSome === 'denySome' ? 'deny' : pWithSome)
+    const p = pWithSome === 'allowSome' ? 'allow' : (pWithSome === 'denySome' ? 'deny' : pWithSome);
     if (!p || p === sign) { continue; }
     if (!sign) {
       sign = p;