allow specifying minimum version for Build-Depends

[rkitover]

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Is your feature request related to a problem? Please describe.
Recently I was upgrading libpng and the build failed because the currently installed version of the zlib port did not have a pkg-config file, while the updated one did, but vcpkg did not know that it had to update zlib first.

Proposed solution
Allow specifying minimum version for dependencies in the Build-Depends: field in CONTROL.

For example:

Build-Depends: zlib>=1.2.11#7

The upgrade command would then check these versions against the installed packages to decide if any build dependencies need to be rebuilt first.