Reorganize build and packages to allow for omitting dev tools

New requirements in our release pipeline require us to omit the installation
of quite a few of our (optional) dev tools, as their post-install tasks
reach out to the public NPM registry and so are blocked. By moving everything
except `esbuild` and `vsce` to `optionalDependencies` (and reorganzing the
build script) we can run the linter and tests outside of the secure container.

Author: andyleejordan

.pipelines/vscode-powershell-Official.yml

@@ -27,7 +27,7 @@ parameters:
 variables:
   system.debug: ${{ parameters.debug }}
   BuildConfiguration: Release
-  WindowsContainerImage: onebranch.azurecr.io/windows/ltsc2019/vse2022:latest
+  WindowsContainerImage: onebranch.azurecr.io/windows/ltsc2022/vse2022:latest
 
 resources:
   repositories:
@@ -50,6 +50,10 @@ extends:
       asyncSdl:
         enabled: true
         forStages: [build]
+    featureFlags:
+      WindowsHostVersion:
+        Version: 2022
+        Network: Netlock
     stages:
     - stage: build
       jobs:
@@ -75,10 +79,6 @@ extends:
             inputs:
               system: Custom
               customVersion: $(package.version)
-          - task: UseNode@1
-            displayName: Use Node 18.x
-            inputs:
-              version: 18.x
           - task: PowerShell@2
             displayName: Install PSResources
             inputs: