Should support polyglot projects better

[testforstephen]

Java projects are not automatically detected when a polyglot project is opened in VS Code. For example, microservice app (e.g. https://github.com/elgris/microservice-app-example) usually places each service into a separate folder, see the structure below. Since the root folder doesn't have any build file, Java extension is not be activated automatically. Every time users have to open a Java file before using any Java feature, which is not convenient.

microservice
├── frontend
│   ...
│   └── package.json
├── backend
│   ...
│   └── pom.xml
└── README

To support polyglot project better, we can relax the activation event a little bit. For example, allow detection of build files from direct subfolders. VS Code activation events support glob pattern, which we can implement using workspaceContains:*/pom.xml. The glob pattern */pom.xml only scans two levels of directories and doesn't add much scanning cost.

    "workspaceContains:*/pom.xml",
    "workspaceContains:*/build.gradle",
    "workspaceContains:*/settings.gradle",
    "workspaceContains:*/build.gradle.kts",
    "workspaceContains:*/settings.gradle.kts",