[F] checkDuplicateTypeName

function checkDuplicateTypeName(
   program,
   type,
   name,
   existing): void

Check the given name is not already specific in the existing map. Report a diagnostic if it is.

Parameters

Parameter	Type	Description
`program`	`Program`	Program
`type`	`Type`	Type with the name to check
`name`	`string`	Name to check
`existing`	`undefined` \| `Record`<`string`, `unknown`>	Existing map of name

void