apiviewgo points out internal/exported pattern

Have it show a message that the `type` from internal is being exported.
"Type `x` is exported from internal. Exported types from internal must be in the ...../internal/exported module"

_Originally posted by @RickWinter in https://github.com/Azure/azure-sdk-tools/pull/8668#discussion_r1688469929_

Start by locating the apiviewgo check that detects types exported from internal and its existing diagnostic tests. Confirm how the message is assembled and add coverage showing the requested warning for an exported internal type, with the issue's prescribed wording and module guidance as the expected result.

Written by the indexing model from the issue text.