Fix issues described in #278, where the path for 15.0 tools is determined when only 16.0 tools are installed.

Description

The logic in ConfigureBuildEnvironment which determines $frameworkDirs was incorrectly including 16.0 (e.g. VS 2019) in it's version lookup. If 16.0+ of VSSetupInstance existed, the $frameworkDir would incorrectly be set to MSBuild\15.0\Bin\amd64.

Change the logic to constrain version search to [15.0, 16.0) for $buildToolsVersions containing "15.0", and allowing [16.0, ] to be considered for "16.0"

Also, include MSBuild 16.0 in the 4.8 environment configuration path.

Related Issue

#278

Motivation and Context

Allows building when only VS 2019 (or tools) are installed.

How Has This Been Tested?

Executed .\build.ps1 Build && .\build.ps1 Test

Locally on two machines -
1 containing VS 2019 Professional only,
1 containing VS 2017 build tools (https://visualstudio.microsoft.com/thank-you-downloading-visual-studio/?sku=BuildTools&rel=15&src=myvs) and VS 2019 Professional

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.