invalidate cache per generation (project-chip#966)

when a user changes configurations, such change might have invalidated some configuration specific setting that has been cached already. By flushing the cache, it enables us to cache SQL results without disregarding user inputs.

src-electron/generator/generation-engine.js

@@ -29,6 +29,7 @@ const dbEnum = require('../../src-shared/db-enum.js')
 const env = require('../util/env')
 const templateEngine = require('./template-engine.js')
 const dbApi = require('../db/db-api.js')
+const dbCache = require('../db/db-cache.js')
 const e = require('express')
 
 /**
@@ -828,6 +829,9 @@ async function generateAndWriteFiles(
     generationLog: null,
   }
 ) {
+  // in case user customization has invalidated the cache
+  dbCache.clear()
+
   let timing = {}
   if (options.fileLoadTime) {
     timing.fileLoad = {
@@ -1066,6 +1070,9 @@ async function contentIndexer(content, linesPerIndex = 2000) {
  * @returns promise that resolves into a preview object.
  */
 async function generateSingleFileForPreview(db, sessionId, outFileName) {
+  // in case user customization has invalidated the cache
+  dbCache.clear()
+
   return queryPackage
     .getSessionPackagesByType(
       db,