Include type reference directives in symlink cache, wait until program is present to create it (#44259)

* Fix discovery of more pnpm symlinks

* Add some tests

* Never show pnpm paths in auto imports, even if there’s no other path

* Import statement completions can return none

* Fix tests

* Add failing test showing poor symlink cache reuse

* Fix test, fails for right reasons now

* Preserve cache built up during program creation, then fill in with program resolutions

* Remove obsolete comment

* Remove obsolete type assertion

* Revert fully filtering out ignored paths

src/compiler/program.ts

@@ -3668,10 +3668,13 @@ namespace ts {
             if (host.getSymlinkCache) {
                 return host.getSymlinkCache();
             }
-            return symlinks || (symlinks = discoverProbableSymlinks(
-                files,
-                getCanonicalFileName,
-                host.getCurrentDirectory()));
+            if (!symlinks) {
+                symlinks = createSymlinkCache(currentDirectory, getCanonicalFileName);
+            }
+            if (files && resolvedTypeReferenceDirectives && !symlinks.hasProcessedResolutions()) {
+                symlinks.setSymlinksFromResolutions(files, resolvedTypeReferenceDirectives);
+            }
+            return symlinks;
         }
     }