Feature request: exclude outDir by default in tsconfig.json

Scenario: As a user, I want typescript compiler to default-exclude output transpiled files to compilerOptions.outDir with compilerOptions.declaration property set to true. I would expect that outDir is excluded by default, because:

• it would prevent me from importing definitions from outDir by error, which is easy to do with intellisense
• it would prevent me from having TS5055 errors such as spotted in #16749 and #6046
• tsc CLI has already implemented this behaviour, see PR #8703

まず PR #8703 と、issues #16749 および #6046 の関連ケースを読み、次に tsconfig.json が compilerOptions.outDir と declaration をどのように扱うかを追跡します。outDir が declarations の有効時にデフォルトで除外されるかどうかを判断し、その動作を関連する compiler tests でカバーできれば完了です。