Library development best practices: detect missing `/sap.ui5/library/i18n: false`

[boghyon]

Is your feature request related to a problem? Please describe.

Similar to #1084, there is an equivalent i18n case.

A library's manifest.json can declare its i18n configuration via the /sap.ui5/library/i18n descriptor entry. When a library ships no translatable texts, this should be set to false. Otherwise, the framework would fall back to requesting multiple resource bundles at runtime unnecessarily that end up with 404.

<lib namespace>/messagebundle_<locale>.properties --> 404
<lib namespace>/messagebundle.properties          --> 404

How the framework interprets /sap.ui5/library/i18n

Value	Meaning
false	Telling that the library has no own resource bundle --> no unnecessary request
true or omitted	messagebundle*.properties requests
URL string	Shorthand for { bundleUrl: "..." } --> requests
object	Requests in accordance with { bundleUrl, bundleName, supportedLocales, fallbackLocale, ... }

Only false prevents bundle loading. Every other value causes the framework to request a bundle. So a library that provides no *.properties bundle but doesn't set i18n: false triggers an avoidable 404.

Describe the solution you'd like

For a project of type "library", warn when all of the following apply:

1. The (generated) manifest.json would not set /sap.ui5/library/i18n to false, and
2. the library ships no matching *.properties file
   --> A resolved *.properties file that is effectively empty (only comments or blank lines) should count as "no i18n" too in my view.

Autofix

Set "i18n": false under /sap.ui5/library in manifest.json:

 {
   "sap.ui5": {
     "library": {
+      "i18n": false