Converge const and regular enums

[vladima]

• const and regular enums use similar rules when evaluating constant expressions. If initializer is not a valid constant expression - this is ok for regular enums but will be an error for const enums.
• is it ok to reference members of other const enums in initializers of const enums, fixes Use const enum values in enum declarations member initializer. #1797
• new undocumented flag 'suppressEnumInlining' blocks inlining of enum values on use sites - this feature was requested externally, fixes LS#getEmitOutput misses constant enum values on second emit #1599

[ahejlsberg]

👍

[vladima]

closed as this is covered by #2199