Rename RealtimeClock to ArduinoTime

The RealtimeClock class is actually managing time so it should be called ArduinoTime

we could also provide a software only implementation which can be useful even if only based on millis() (there are a number of use cases where one needs to manage time, maybe syncronising via NTP every etc)

首先在 ArduinoCore-API 源代码中定位 RealtimeClock 类，并查看关于拟议重命名和纯软件实现的 issue 评论。完成的标准是：该类已统一重命名为 ArduinoTime，已提供约定的软件支持时间实现，并已更新相关的现有检查。

由索引模型根据 Issue 内容生成。