ConVars: utilize globals for CreateConVar flags

[EntranceJew]

Is your feature request related to a problem? Please describe. Consolidate CreateConVar flags into client/server constants. There's reasonably only a few configurations that matter:

• SERVER-only: FCVAR_ARCHIVE, FCVAR_NOTIFY
• CLIENT-only: FCVAR_ARCHIVE
• SHARED: FCVAR_ARCHIVE, FCVAR_NOTIFY, FCVAR_REPLICATED

Odds and ends:

• Rarely, things are marked as FCVAR_CHEAT but those are concommands.
• ttt_damage_own_healthstation has FCVAR_NONE set, which seems like a mistake.
• sh_equip_items.lua has FCVAR_SERVER_CAN_EXECUTE on server-only convars, which doesn't matter if the client doesn't have them defined.
• A few client-exclusive convars have FCVAR_USERINFO but there's no point in this value being sent to the server if it can't be read. Could be harmlessly added to CLIENT-only scope.
• No other FCVAR variant is utilized in the code.

Describe the solution you'd like Add values to the global scope for re-use, so that the intent can be compared against the realm of the CreateConVar declaration.

• CV_FLAGS_SERVER = bit.bor(FCVAR_ARCHIVE, FCVAR_NOTIFY)
• CV_FLAGS_CLIENT= FCVAR_ARCHIVE
• CV_FLAGS_SHARED = bit.bor(FCVAR_ARCHIVE, FCVAR_NOTIFY, FCVAR_REPLICATED)

Describe alternatives you've considered This seems pretty reasonable, I can't imagine anything more clear. A way to define a CreateConVar with an appropriate language string would be nice, but because the localizations exist in the MENU/CLIENT state it's not always possible for the SERVER to use them.

Additional context A lot of things broke recently because some silent error handling for ClientCreateConVar stopped happening, and it brought it to my attention to pay more attention to what gets applied when.