Don't count a write-only reference as a use (#17752)

* Don't count a write-only reference as a use

* Split isWriteAccess to isWriteOnlyAccess and isReadOnlyAccess

* Update "unusedParameterUsedInTypeOf" to use "b"

* Update diagnostic messages: "is never used" -> "its value is never read"

* Use a WriteKind enum

* Rename enum and move documentation to enum members

src/server/server.ts

@@ -585,7 +585,6 @@ namespace ts.server {
     function createPollingWatchedFileSet(interval = 2500, chunkSize = 30) {
         const watchedFiles: WatchedFile[] = [];
         let nextFileToCheck = 0;
-        let watchTimer: any;
         return { getModifiedTime, poll, startWatchTimer, addFile, removeFile };
 
         function getModifiedTime(fileName: string): Date {
@@ -622,7 +621,7 @@ namespace ts.server {
         // stat due to inconsistencies of fs.watch
         // and efficiency of stat on modern filesystems
         function startWatchTimer() {
-            watchTimer = setInterval(() => {
+            setInterval(() => {
                 let count = 0;
                 let nextToCheck = nextFileToCheck;
                 let firstCheck = -1;