* Quick fix: Simplify devBuilds.yml
- remove an excess build step
* Quick fix: Move `SetupNugetSources` script invocations above `parameters.beforeBuild`
- ensure NuGet.config is ready for all internal builds
- remove now-duplicate `SetupNugetSources` invocations wherever default-build.yml is used
* Quick fix: Clean up SiteExtensions/build.cmd
- quote all rooted paths
- check `%ERRORLEVEL%` after every `CALL`
- nits:
- add a few more `ECHO` commands
- wrap long lines
* Quick fix: Ensure `$(BuildNative)` is always set correctly
- fix problems using `-all` or `/p:BuildAllProjects=true` without `-buildNative`
- ensure `$(BuildNative)` is `false` where it's not supported
- move some duplicated settings into eng/Common.props and `<Import />` the new file
- remove now-duplicated parts of conditions using `$(BuildNative)`
* Quick fix: Consistently use `--build-*`
- avoid `/p:Build*` on the command line (except with eng/scripts/ci-source-build.sh)
- nits:
- remove now-useless `-buildNative` with `-all`
- expand and correct a couple of related comments and messages
* Quick fix: Support `-all` together with `-projects`
- remove need to specify `/p:BuildAllProjects=true`
- nit: simplify some Boolean logic