Package Validation Options

[kieronlanning]

Strict Mode

Add a strict mode that when enabled fails when anything is additional - i.e. unexpected - in the package.

The recent globing support still allows for things like ./.agents/** so we don't need to list everything out.

TFM Checks/ Placeholders

Add support for validating specific TFMs, with placeholder support, so we can say ./lib/{TFM}/some/path/Assembly.dll instead of ./lib/*/some/path/Assembly.dll or ./lib/**/Assembly.dll.