Docs: added code comments for everything in the @grafana/runtime package. (#23456)

* added comments for the angular loader.

* added code documentation for backendSrv.

* docs for datasource_srv.

* added some more docs.

* added documentation for the locationsrv.

* started to add docs for echo srv.

* added docs for meta srv.2

* added docs for analytics.

* draft documentation of the DataSourceWithBackend.

* added docs for last files.

* fixed all warnigns in api-extractor.

* fixed some typos and captializations.

api-extractor.json

@@ -23,6 +23,10 @@
     "extractorMessageReporting": {
       "default": {
         "logLevel": "warning"
+      },
+      "ae-internal-missing-underscore": {
+        "logLevel": "none",
+        "addToApiReportFile": false
       }
     },
     "tsdocMessageReporting": {