Move single use function in line (#82885)

## Summary

 * Function rename to follow existing get/fetch convention
    ```diff
    - export async function loadRegistryPackage(
    + export async function getRegistryPackage(
    ```
 * Moved `unpackRegistryPackageToCache` into `getRegistryPackage`
    * In my opinion, those three/four statements are more clear than the previous name
    * It isn't used anywhere else

x-pack/plugins/ingest_manager/server/services/epm/packages/get.ts

@@ -116,7 +116,7 @@ export async function getPackageInfo(options: {
   ] = await Promise.all([
     getInstallationObject({ savedObjectsClient, pkgName }),
     Registry.fetchFindLatestPackage(pkgName),
-    Registry.loadRegistryPackage(pkgName, pkgVersion),
+    Registry.getRegistryPackage(pkgName, pkgVersion),
   ]);
 
   // add properties that aren't (or aren't yet) on Registry response

x-pack/plugins/ingest_manager/server/services/epm/packages/install.ts

@@ -248,7 +248,7 @@ export async function installPackageFromRegistry({
     throw new PackageOutdatedError(`${pkgkey} is out-of-date and cannot be installed or updated`);
   }
 
-  const { paths, registryPackageInfo } = await Registry.loadRegistryPackage(pkgName, pkgVersion);
+  const { paths, registryPackageInfo } = await Registry.getRegistryPackage(pkgName, pkgVersion);
 
   const removable = !isRequiredPackage(pkgName);
   const { internal = false } = registryPackageInfo;

x-pack/plugins/ingest_manager/server/services/epm/registry/index.ts

@@ -20,7 +20,6 @@ import {
 } from '../../../types';
 import { unpackArchiveToCache } from '../archive';
 import { cacheGet, getArchiveFilelist, setArchiveFilelist } from '../archive';
-import { ArchiveEntry } from './extract';
 import { fetchUrl, getResponse, getResponseStream } from './requests';
 import { streamToBuffer } from './streams';
 import { getRegistryUrl } from './registry_url';
@@ -126,27 +125,18 @@ export async function fetchCategories(params?: CategoriesParams): Promise<Catego
   return fetchUrl(url.toString()).then(JSON.parse);
 }
 
-export async function unpackRegistryPackageToCache(
-  pkgName: string,
-  pkgVersion: string,
-  filter = (entry: ArchiveEntry): boolean => true
-): Promise<string[]> {
-  const { archiveBuffer, archivePath } = await fetchArchiveBuffer(pkgName, pkgVersion);
-  const contentType = mime.lookup(archivePath);
-  if (!contentType) {
-    throw new Error(`Unknown compression format for '${archivePath}'. Please use .zip or .gz`);
-  }
-  const paths: string[] = await unpackArchiveToCache(archiveBuffer, contentType);
-  return paths;
-}
-
-export async function loadRegistryPackage(
+export async function getRegistryPackage(
   pkgName: string,
   pkgVersion: string
 ): Promise<{ paths: string[]; registryPackageInfo: RegistryPackage }> {
   let paths = getArchiveFilelist(pkgName, pkgVersion);
   if (!paths || paths.length === 0) {
-    paths = await unpackRegistryPackageToCache(pkgName, pkgVersion);
+    const { archiveBuffer, archivePath } = await fetchArchiveBuffer(pkgName, pkgVersion);
+    const contentType = mime.lookup(archivePath);
+    if (!contentType) {
+      throw new Error(`Unknown compression format for '${archivePath}'. Please use .zip or .gz`);
+    }
+    paths = await unpackArchiveToCache(archiveBuffer, contentType);
     setArchiveFilelist(pkgName, pkgVersion, paths);
   }
 
@@ -194,7 +184,7 @@ export async function ensureCachedArchiveInfo(
   const paths = getArchiveFilelist(name, version);
   if (!paths || paths.length === 0) {
     if (installSource === 'registry') {
-      await loadRegistryPackage(name, version);
+      await getRegistryPackage(name, version);
     } else {
       throw new PackageCacheError(
         `Package ${name}-${version} not cached. If it was uploaded, try uninstalling and reinstalling manually.`