Summary: Allow Point p = new (x, y);

Shipped in preview in 16.7p1.

• Proposal added
• Discussed in LDM
• Decision in LDM (let's go ahead with prototype)
• Finalized (done, rejected, inactive)
• Spec'ed

See also dotnet/roslyn#35

• https://github.com/dotnet/csharplang/blob/master/meetings/2018/LDM-2018-05-21.md
• https://github.com/dotnet/csharplang/blob/master/meetings/2018/LDM-2018-06-25.md
• https://github.com/dotnet/csharplang/blob/master/meetings/2018/LDM-2018-08-22.md#target-typed-new
• https://github.com/dotnet/csharplang/blob/master/meetings/2018/LDM-2018-10-17.md
• https://github.com/dotnet/csharplang/blob/master/meetings/2018/LDM-2018-10-17.md#target-typed-new

Test plan: dotnet/roslyn#28489