Add `workspaceContains` and `onView` to extension `activationEvents` in `package.json` about evidence-vscode

[RandomFractals]

After reading workspaceContains activation even docs, we now know why our .evidence glob pattern did not work. That activation kicks in only when the folder is open:

This activation event is emitted and interested extensions will be activated whenever a folder is opened and the folder contains at least one file that matches a glob pattern.

"activationEvents": [
    "workspaceContains:**/.editorconfig"
]

So, I think we'll just check for **/package.json to activate extension.

After activation we can check if that config has evidence dependencies and exit gracefully, if it's just another web app project.

[RandomFractals]

We can also use onView activation event and check if the built-in simpler browser we are using is open, which happens when you close vscode after viewing evidence app page. Simple browser uses simpleBrowser.view id.

Docs: https://code.visualstudio.com/api/references/activation-events#onView

[RandomFractals]

Reopening Evidence project with an active Simple Browser view should now enable Evidence start and other custom commands:

[RandomFractals]

The other checks we already perform in Evidence ext. activation code and in #43

  // check for evidence app files and node modules
  const packageJson = await loadPackageJson();
  const evidenceFiles = await workspace.findFiles('**/.evidence/**/*.*');
  if (workspace.workspaceFolders && evidenceFiles.length > 0 &&
    hasDependency(packageJson, '@evidence-dev/evidence')) {
    updateProjectContext();

    // check for node modules
    const nodeModules = await workspace.findFiles('**/node_modules/**/*.*');
    if (nodeModules.length > 0) {
      // show start dev server status
      statusBar.showStart();
    }
    else {
      // show install node modules status
      statusBar.showInstall();
    }
  }