Use @kbn/handlebars and compileAST over handlebars.compile (#218449)

## Summary

Change usage of Handlebars.compile across Kibana to use
`@kbn/handlebars` and `compileAST`

### Note for reviewers:
There should be no change for the rendered output where it's used.
Wherever there were tests, i ensured they were passing after making the
change.

### Checklist

Check the PR satisfies following conditions. 
Reviewers should verify this PR satisfies this list as well.

- [ ] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios

---------

Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>
Co-authored-by: kibanamachine <42973632+kibanamachine@users.noreply.github.com>

x-pack/platform/plugins/shared/fleet/server/services/epm/agent/agent.ts

@@ -5,7 +5,7 @@
  * 2.0.
  */
 
-import Handlebars from 'handlebars';
+import Handlebars from '@kbn/handlebars';
 import { load, dump } from 'js-yaml';
 import type { Logger } from '@kbn/core/server';
 
@@ -30,7 +30,7 @@ export function compileTemplate(variables: PackagePolicyConfigRecord, templateSt
     let template = getHandlebarsCompiledTemplateCache(templateStr);
 
     if (!template) {
-      template = handlebars.compile(templateStr, { noEscape: true });
+      template = handlebars.compileAST(templateStr, { noEscape: true });
       setHandlebarsCompiledTemplateCache(templateStr, template);
     }
 

x-pack/platform/plugins/shared/fleet/server/services/epm/packages/cache.test.ts

@@ -5,7 +5,7 @@
  * 2.0.
  */
 
-import Handlebars from 'handlebars';
+import Handlebars from '@kbn/handlebars';
 
 import {
   getPackageAssetsMapCache,
@@ -40,7 +40,7 @@ describe('EPM CacheSession', () => {
 
     it('should not cache handlebars template', () => {
       const template1 = `test1: {{test}}`;
-      setHandlebarsCompiledTemplateCache(template1, handlebars.compile(template1));
+      setHandlebarsCompiledTemplateCache(template1, handlebars.compileAST(template1));
       const cache1 = getHandlebarsCompiledTemplateCache(template1);
       expect(cache1).toBeUndefined();
     });
@@ -85,9 +85,9 @@ describe('EPM CacheSession', () => {
     it('should cache handle template', async () => {
       function setCache() {
         const template1 = `test1: {{test}}`;
-        setHandlebarsCompiledTemplateCache(template1, handlebars.compile(template1));
+        setHandlebarsCompiledTemplateCache(template1, handlebars.compileAST(template1));
         const template2 = `test2: {{test}}`;
-        setHandlebarsCompiledTemplateCache(template2, handlebars.compile(template2));
+        setHandlebarsCompiledTemplateCache(template2, handlebars.compileAST(template2));
       }
       function getCache() {
         const template1 = `test1: {{test}}`;

x-pack/platform/plugins/shared/fleet/server/services/epm/packages/cache.ts

@@ -9,6 +9,8 @@ import { AsyncLocalStorage } from 'async_hooks';
 
 import { LRUCache } from 'lru-cache';
 
+import type { TemplateDelegate } from '@kbn/handlebars';
+
 import type { AssetsMap, PackagePolicyAssetsMap } from '../../../../common/types';
 
 import type { PackageInfo } from '../../../../common';
@@ -27,7 +29,7 @@ class CacheSession {
 
   private _agentTemplateAssetsMap?: LRUCache<string, PackagePolicyAssetsMap>;
 
-  private _handlebarsCompiledTemplate?: LRUCache<string, HandlebarsTemplateDelegate>;
+  private _handlebarsCompiledTemplate?: LRUCache<string, TemplateDelegate>;
 
   private _isSpaceAwarenessEnabledCache?: boolean;
 
@@ -60,7 +62,7 @@ class CacheSession {
 
   getHandlebarsCompiledTemplateCache() {
     if (!this._handlebarsCompiledTemplate) {
-      this._handlebarsCompiledTemplate = new LRUCache<string, HandlebarsTemplateDelegate>({
+      this._handlebarsCompiledTemplate = new LRUCache<string, TemplateDelegate>({
         max: HANDLEBARS_COMPILE_TEMPLATE_CACHE_SIZE,
       });
     }
@@ -128,10 +130,7 @@ export function getHandlebarsCompiledTemplateCache(tplStr: string) {
   return cacheStore.getStore()?.getHandlebarsCompiledTemplateCache()?.get(tplStr);
 }
 
-export function setHandlebarsCompiledTemplateCache(
-  tplStr: string,
-  tpl: HandlebarsTemplateDelegate
-) {
+export function setHandlebarsCompiledTemplateCache(tplStr: string, tpl: TemplateDelegate) {
   return cacheStore.getStore()?.getHandlebarsCompiledTemplateCache()?.set(tplStr, tpl);
 }
 

x-pack/platform/plugins/shared/fleet/tsconfig.json

@@ -120,5 +120,6 @@
     "@kbn/core-security-server",
     "@kbn/core-http-server-utils",
     "@kbn/core-notifications-browser-mocks",
+    "@kbn/handlebars",
   ]
 }