Use private properties, optional chaining & coalescing operator

Just a syntactic refactoring, makes no difference for consumers. The
syntax is supported by all our target environments, but if browserify
is used (without babel or similar) it'll fail to parse. Not sure if
that constitutes a breaking change.

Category: change

.airtap.yml

@@ -12,3 +12,8 @@ presets:
       - airtap-electron
     browsers:
       - name: electron
+
+# Until airtap switches to rollup
+browserify:
+  - transform: babelify
+    presets: ["@babel/preset-env"]

.github/dependabot.yml

@@ -7,10 +7,12 @@ updates:
     ignore:
       - dependency-name: standard
       - dependency-name: ts-standard
-      - dependency-name: '@types/node'
+      - dependency-name: "@types/node"
       - dependency-name: voxpelli/tsconfig
       - dependency-name: typescript
       - dependency-name: hallmark
+      - dependency-name: "@babel/preset-env"
+      - dependency-name: babelify
 
       # Stay on the 3rd or 4th oldest stable release, per
       # https://www.electronjs.org/docs/latest/tutorial/electron-timelines#version-support-policy