* Disambiguate icon for daily builds on Windows.
Some code had to be borrowed from build.psm1 because this script has to be self contained in case it gets executed by only downloading this file via the published download link https://twitter.com/Steve_MSFT/status/930585082451992576
1. Remove `[validate]` attribute from parameter so this script can be invoked directly from the web. This doesn't have any negative impact as the $Destination parameter will have a default value if null or empty.
2. Move removal of destination folder later as installing the package requires package management module and archive module (on Windows)
3. On Windows, because files have open handles when run from existing powershell-daily install, I rename the existing files and copy over the new ones. User needs to exit and restart `pwsh` to take effect (similar to macOS/Linux where you have to exit and restart anyways)
Enhance 'install-powershell.ps1' to work on Linux and macOS too. A user can install release version or daily powershell core on Linux and macOS.
When `-AddToPath` is specified:
- On Windows, add the absolute destination path to the 'User' scope environment variable 'Path';
- On Linux, make the symlink '/usr/bin/pwsh' points to "$Destination/pwsh";
- On MacOS, make the symlink '/usr/local/bin/pwsh' points to "$Destination/pwsh".
- Add install-powershell.ps1 to install powershell core packages on windows.
- Update Start-PSBootStrap to check and install the latest PSCore package on Windows.
