build: bootstrap vcpkg before nuget restore (#17592)

`nuget restore` actually runs through MSBuild! However, #15855 added a
dependency from our project on a system-installed _or locally detected_
`vcpkg.targets` (or `.props`).

Our build runs `nuget restore` before finding or installing vcpkg, so
the rules in our project file would try to import vcpkg before it had
been found (or installed).

On build agents with vcpkg installed via the VS workload, this was fine:
we would import the one that came with VS and go on our merry way. On
build agents where it needs to be installed locally, it could not be
imported.

The fix in this PR is to install/bootstrap vcpkg before running nuget.

I tried to isolate the vcpkg rules to only run _in the absence of
nuget_, but that didn't work.

Author: DHowett

build/pipelines/templates-v2/job-build-project.yml

@@ -159,10 +159,10 @@ jobs:
       .\build\scripts\Generate-ThirdPartyNotices.ps1 -MarkdownNoticePath .\NOTICE.md -OutputPath .\src\cascadia\CascadiaPackage\NOTICE.html
     displayName: Generate NOTICE.html from NOTICE.md
 
-  - template: .\steps-restore-nuget.yml
-
   - template: .\steps-install-vcpkg.yml
 
+  - template: .\steps-restore-nuget.yml
+
   - pwsh: |-
       .\build\scripts\Set-LatestVCToolsVersion.ps1
     displayName: Work around DD-1541167 (VCToolsVersion)