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/server/project.ts

@@ -353,10 +353,15 @@ namespace ts.server {
 
         /*@internal*/
         getSymlinkCache(): SymlinkCache {
-            return this.symlinks || (this.symlinks = discoverProbableSymlinks(
-                this.program?.getSourceFiles() || emptyArray,
-                this.getCanonicalFileName,
-                this.getCurrentDirectory()));
+            if (!this.symlinks) {
+                this.symlinks = createSymlinkCache(this.getCurrentDirectory(), this.getCanonicalFileName);
+            }
+            if (this.program && !this.symlinks.hasProcessedResolutions()) {
+                this.symlinks.setSymlinksFromResolutions(
+                    this.program.getSourceFiles(),
+                    this.program.getResolvedTypeReferenceDirectives());
+            }
+            return this.symlinks;
         }
 
         // Method of LanguageServiceHost