…eline

Currently hosted agents on Azure DevOps don't support 10.0.18362.0 yet.

This variable is not defined when building a single project, for example in the build
pipelines. Instead use a relative path to the current project for the same effect.

Some native include paths in webrtc-uwp-sdk were using junctions which are only available
if the webrtc.lib compiling script ran. Use instead the actual junction target path for build
pipelines which don't have those junctions.

Several directories from this path are aliased into webrtc/xplatform/webrtc via junctions,
which are not available on build agents.

Add a 6-hour timeout on the job, the maxmium, in addition of the
individual timeouts on each step, to prevent Azure from killing the
build midway through WinRT wrappers compiling.

Initial commit of Azure pipeline config