Add Number value literal lookahead restrictions

[michaelstaib]

Update the Utf8GraphQLReader (lexer) to correctly distinguish between name, int and float tokens.

https://github.com/ChilliCream/hotchocolate/blob/master/src/Core/Language/Utf8/Utf8GraphQLReader.cs

Follow RFC over at the spec repo:
graphql/graphql-spec#601

[michaelstaib]

This is where we should do a look ahead:
https://github.com/ChilliCream/hotchocolate/blob/090a84bc9271e2a1bee67f9f22755dd84e4c18c7/src/Core/Language/Utf8/Utf8GraphQLReader.cs#L256

[michaelstaib]

graphql/graphql-spec#599

[michaelstaib]

graphql/graphql-spec#601