Opting out for specific known content types

There should be a way to opt of validation for specific know content types.

The issue arises relates to this issue raised for PDE:

https://github.com/eclipse-pde/eclipse.pde/issues/294

PDE has abused the XML Schema namespace for its own purpose leading to all kinds of validation errors that are not really errors for PDE's actual use of *.exsd resources.

Similarly a PDE *.target file doesn't specify a schema, but the editor knows the correct structure so a warning about the schema being missing is just noise to the user. Same for feature.xml, category.xml, plugin.xml, and *.product.

The Lemminx functionality is generally very cool and very useful, but it seems the only way to disable this for PDE's resources is to disable it in general, which definitely not desired either. Apparently the issue should not be addressed in LemMinx, as suggested by this comment:
https://github.com/eclipse-pde/eclipse.pde/issues/294#issuecomment-1216550919

but rather in Wild Web Developer as suggested by this comment:

https://github.com/eclipse/lemminx/issues/1275#issuecomment-1221371932

まず、リンクされている PDE #294 と LemMinx #1275 の議論を読み、Wild Web Developer と LemMinx の境界を理解します。Wild Web Developer がコンテンツタイプと検証をどこで処理しているかを特定し、完了条件を、他の XML ファイルの検証を無効にすることなく、一覧にある PDE リソースに対するスキーマ関連の警告を抑制することと定義します。