chore: use consistent file naming

packages/reactivity/src/computed.ts

@@ -2,7 +2,7 @@ import { ReactiveEffect } from './effect'
 import { Ref, trackRefValue, triggerRefValue } from './ref'
 import { isFunction, NOOP } from '@vue/shared'
 import { ReactiveFlags, toRaw } from './reactive'
-import { Dep } from './Dep'
+import { Dep } from './dep'
 
 export interface ComputedRef<T = any> extends WritableComputedRef<T> {
   readonly value: T

packages/reactivity/src/effect.ts

@@ -8,7 +8,7 @@ import {
   initDepMarkers,
   newTracked,
   wasTracked
-} from './Dep'
+} from './dep'
 
 // The main WeakMap that stores {target -> key -> dep} connections.
 // Conceptually, it's easier to think of a dependency as a Dep class

packages/reactivity/src/ref.ts

@@ -3,7 +3,7 @@ import { TrackOpTypes, TriggerOpTypes } from './operations'
 import { isArray, isObject, hasChanged } from '@vue/shared'
 import { reactive, isProxy, toRaw, isReactive } from './reactive'
 import { CollectionTypes } from './collectionHandlers'
-import { createDep, Dep } from './Dep'
+import { createDep, Dep } from './dep'
 
 export declare const RefSymbol: unique symbol