CodeHealth: Stop using Deprecated DictionaryValues methods in ash

Replaces `DictionaryValue::HasKey()` with `Value::FindKey()`
Replaces `DictionaryValue::DeepCopy()` with `Value::Clone()`
Replaces `DictionaryValue::SetBoolean()` with `Value::SetBoolKey()`
Replaces `DictionaryValue::Get()` with `Value::FindKey()`
Replaces `DictionaryValue::Set()` with `Value::SetKey()`

Removed the use of base::DictionaryValue inside shelf_prefs as well.

Bug: 1187060,1187058,1187025,1187032,1187023,1187061
Change-Id: Ia37f8d3ecefb542ab013f06220164f6e467bbd6b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3379923


Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Min Chen <minch@chromium.org>
Cr-Commit-Position: refs/heads/main@{#958144}