Make PTVS build for Dev18

[StellaHuang95]

• [x] Update Source Code Build Configuration for Dev18

  • [x] Build Configuration Files
  • [x] C++ Project Files (vcxproj files)
  • [x] C# Project Files (.csproj files)
  • [x] Package Configuration
  • [x] Assembly Version Files
  • [x] VSIX Manifest

• [ ] Build Pipelines: Update azure-pipelines.yml, release, and compliance pipeline configurations.

  The current build pipeline uses the MSBuild@1 Azure task, which doesn't yet support Dev18. While the MSBuild command-line tool already supports Dev18 builds, we're waiting for Azure Pipeline task support.

  Track progress at https://github.com/microsoft/azure-pipelines-tasks/issues/21319

• [x] Update VS Bootstrapper Configuration

  The build pipeline currently generates a Dev17 Visual Studio installer with the latest PTVS changes for testing purposes. This needs to be updated for Dev18.

  • [x] Update create_vs_bootstrapper.yml
  • [x] Coordinate with CTI: Notify the team that the bootstrapper will now generate Dev18 installer bits instead of Dev17

• [x] Snap PTVS Main to Dev17 Release Branch

  • [ ] Create branch protection rules for the release branch

  Currently, all changes flowing into Visual Studio main are targeting Dev18. Since the VS team has already snapped their main branch to the Dev17 release branch, we should also create a clear separation between Dev17 and Dev18 development streams.

  This maintains stable Dev17 releases and also enables parallel Dev18 development.

• [x] Update the Build and Debug Instructions for PTVS: https://github.com/microsoft/PTVS/wiki/Build-and-Debug-Instructions-for-PTVS

• [ ] Address Dev18-Specific Issues

  • [x] https://devdiv.visualstudio.com/DevDiv/_workitems/edit/2416924
  • [ ] https://github.com/microsoft/PTVS/issues/8276
  • [x] https://github.com/microsoft/PTVS/issues/8277
  • [x] https://github.com/microsoft/PTVS/issues/8290
  • [x] https://github.com/microsoft/PTVS/issues/8291

[rizi]

@StellaHuang95 wouldn't it make sense that the tasks just use the latest installed version of VS/MsBuild? At the moment the tasks needs to be updated to support new version of VS. Also within the tasks "use latest version" is quite misleading, because it means the latest version of VS that is supported by the task and not the latest installed version