Re-name Preview VSIX to "Windows App SDK (Experimental)" for 1.0 exp release

[anawishnoff]

Describe the bug

For the 1.0 experimental release, we will be shipping it out using this VSIX: Project Reunion (Preview). This VSIX should be renamed to Windows App SDK (Experimental) to ensure consistency with our official name and with our release channels.

FYI @BenJKuhn, @axelandrejs