[WeakLookupTable] Rename the tuple label in return type of _findHole

Rename 'found' to 'alreadyExists'. 'found' implies that we found a hole which
we will always do.

Author: rintaro

Sources/SwiftSyntax/WeakLookupTable.swift

@@ -109,7 +109,8 @@ class WeakLookupTable<Element: Identifiable & AnyObject> {
 
   /// Finds the bucket where the object with the specified id should be stored
   /// to.
-  private func _findHole(_ id: Element.Identifier) -> (pos: Int, found: Bool) {
+  private
+  func _findHole(_ id: Element.Identifier) -> (pos: Int, alreadyExists: Bool) {
     var bucket = _idealBucket(for: id)
 
     // Starting from the ideal bucket for the id, search an available bucket,
@@ -190,8 +191,8 @@ class WeakLookupTable<Element: Identifiable & AnyObject> {
   /// Inserts the given object into the table.
   @discardableResult
   func insert(_ obj: Element) -> Bool {
-    var (pos, found) = _findHole(obj.id)
-    if found {
+    var (pos, alreadyExists) = _findHole(obj.id)
+    if alreadyExists {
       return false
     }