plugin: findFiles should handle ignored files

The following commit updates the `findFiles` plugin API to respect
`exclude: null` which indicates that the search should yield results in
all files (no exclude or ignored constraints).

Signed-off-by: vince-fugnitto <vincent.fugnitto@ericsson.com>

packages/plugin-ext/src/main/browser/workspace-main.ts

@@ -166,7 +166,14 @@ export class WorkspaceMainImpl implements WorkspaceMain, Disposable {
         for (const rootUri of rootUris) {
             roots[rootUri] = {};
         }
-        const opts: FileSearchService.Options = { rootOptions: roots };
+        const useGitIgnore: boolean = !(
+            typeof excludePatternOrDisregardExcludes === 'boolean' &&
+            excludePatternOrDisregardExcludes === false
+        );
+        const opts: FileSearchService.Options = {
+            rootOptions: roots,
+            useGitIgnore
+        };
         if (includePattern) {
             opts.includePatterns = [includePattern];
         }