Champion "allow digit separator after 0b or 0x" (C# 7.2, VB 15.5)

[gafter]

• [X] Proposal added https://github.com/dotnet/csharplang/blob/master/proposals/csharp-7.2/leading-separator.md
• [x] Discussed in LDM
• [x] Decision in LDM
• [x] Finalized (done, rejected, inactive)
• [ ] Spec'ed

(from https://github.com/dotnet/roslyn/issues/12680)

See PR https://github.com/dotnet/roslyn/pull/20449 (implemented in 15.5)

[gafter]

Thanks to @alrz for implementing this feature!

[gafter]

I added

https://github.com/dotnet/csharplang/blob/master/proposals/csharp-7.2/leading-separator.md

which will serve as a spec.

[alrz]

From this blog post:

// still invalid
var c = 10_.0;  // error: next to decimal
var d = 1.1e_1; // error: next to exponent character
var e = 10_f;   // error: next to type specified

Makes sense, but probably not important enough to do yet another iteration on separators.