Prefer const wherever possible

Summary:
Non-final identifiers make code harder to understand.
This is particularly true for JavaScript where even the *type*
can change as a value gets reassigned later.

This enforces to use `const` whereever possible, but doesn't
"outlaw" `let`. Mixed destructuring is also still allowed.

Used `eslint --fix` to change all existing cases.

Reviewed By: jknoxville

Differential Revision: D16131329

fbshipit-source-id: 2eceaca7c603b71b36e005be5d135e1849f2518d

src/utils/pluginUtils.js

@@ -46,12 +46,12 @@ export function getPersistedState<PersistedState>(
 }
 
 export function getActivePluginNames(plugins: PluginsState): Array<string> {
-  let pluginsMap: Map<
+  const pluginsMap: Map<
     string,
     Class<FlipperDevicePlugin<> | FlipperPlugin<>>,
   > = pluginsClassMap(plugins);
 
-  let arr: Array<PluginDefinition> = plugins.disabledPlugins.concat(
+  const arr: Array<PluginDefinition> = plugins.disabledPlugins.concat(
     plugins.gatekeepedPlugins,
   );
   arr.forEach((plugin: PluginDefinition) => {