[Display] 添加固定设计/渲染分辨率的画布模式，避免繁琐的渲染分辨率处理

[Demonese]

固定设计/渲染分辨率的画布模式其实在很多 2D 游戏（比如 galgame）和弹幕风中都有使用，其特征为，画布大小固定，渲染分辨率固定，且对平台相关的窗口大小、显示设置等无感知，也与它们无关。

由于该改动过于巨大，可能会涉及引擎大量组件的更改和 Lua API 的巨大变动，计划开一个新分支用来实现该特性。

设计上：

• 窗口显示模式大改， 不再支持显式指定窗口大小， 窗口大小也不再固定，允许自由调整大小
• 全屏显示模式大改，自动选择合适的方式进行全屏显示，且不再支持显式切换独占全屏
  • 1、对于 Windows 10 1809 及以上的系统，采用 DirectComposition 底层系统 API 进行独占全屏模式显示，以获得最高的效率
  • 2、根据设置的画布大小，挑选适配的显示模式，尝试进入传统独占全屏模式
  • 3、在第 2 条失败的情况下，对于 Windows 8.1 及以上的系统，采用 DirectComposition 底层系统 API 进行全屏无边框窗口显示，以获得最高的效率（已放弃，它在 Windows 8.1 上并不比传统的全屏无边框窗口好）
  • 4、在第 3 条不满足的情况下，回退到传统的全屏无边框窗口进行显示
• 变更 Lua API 的行为：
  • 显示框架变更：
    • lstg.SetWindowed 允许运行时调用，且切换全屏显示模式时不再直接进入独占全屏模式，而是自动选择最优的全屏模式（暂时不改，维持 API 行为一致性）
    • lstg.SetVsync 允许运行时调用（暂时不改，维持 API 行为一致性）
    • lstg.SetResolution 允许运行时调用，且不再修改窗口大小，而是修改画布大小（暂时不改，维持 API 行为一致性）
    • lstg.EnumResolutions 被废弃
    • lstg.ChangeVideoMode 不再修改窗口大小，而是修改画布大小，切换全屏模式时不再直接进入独占全屏模式，而是自动选择最优的全屏模式（此 API 的行为表现上应该和以前不会有差别，即使实际行为已改变）
  • 鼠标输入变更：
    • lstg.GetMousePosition 获取的鼠标坐标是相对画布的
    • lstg.Input.Mouse.GetPosition 获取的鼠标坐标是相对画布的
  • 渲染器变更：
    • lstg.CreateRenderTarget 创建的“自动大小”（不填写大小参数）渲染目标，其大小和画布的相同，而不是和窗口的相同
    • lstg.SetImageScale 不再支持修改全局渲染缩放（为了兼容，可以不抛出错误，而是打印警告）（暂时不改，维持 API 行为一致性）
    • lstg.Snapshot 固定截取画布的内容

进度：

• [x] 方案设计
• [x] 测试版开发
• [x] 公开测试
• [ ] 发布正式版，并宣布特性为稳定（stable）

[Demonese]

[Feature] Add a canvas mode with fixed design/rendering resolution to avoid complex rendering resolution setup

The canvas mode with fixed design/rendering resolution is actually used in many 2D games (such as galgame) and dnh engine. Its characteristic is that the canvas size is fixed and the rendering resolution is fixed. It is not aware of, and has nothing to do with, platform-dependent window sizes, display settings, etc.

Since the change is too large, it may involve changes in a large number of engine components and a huge change in the Lua API. It is planned to create a new branch to implement this feature.

Design:

• The window display mode has been greatly changed. It no longer supports explicitly specifying the window size, and the window size is no longer fixed, allowing free resizing
• The full-screen display mode has been greatly changed, and the appropriate method is automatically selected for full-screen display, and explicit switching to exclusive full-screen is no longer supported
  1. For Windows 10 1809 and above systems, use the DirectComposition underlying system API for exclusive full-screen mode display to obtain the highest efficiency
  2. According to the set canvas size, select an adapted display mode, and try to enter the traditional exclusive full-screen mode
  3. In the case of the failure of option 2, for Windows 8.1 and above systems, use the DirectComposition underlying system API for full-screen borderless window display to obtain the highest efficiency (Abandoned, it is no better than the traditional full-screen borderless window on Windows 8.1)
  4. If option 3 is not satisfied, fall back to the traditional full-screen borderless window for display
• Change the behavior of the Lua API:
  • Show frame changes:
    • lstg.SetWindowed is allowed to be called at runtime, and when switching the full-screen display mode, it no longer directly enters the exclusive full-screen mode, but automatically selects the optimal full-screen mode (keep consistency of API behavior)
    • lstg.SetVsync allows runtime calls to (keep consistency of API behavior)
    • lstg.SetResolution allows runtime calls, and no longer modifies the window size, but modifies the canvas size (keep consistency of API behavior)
    • lstg.EnumResolutions is deprecated
    • lstg.ChangeVideoMode no longer modifies the window size, but modifies the canvas size. When switching full-screen mode, it no longer directly enters the exclusive full-screen mode, but automatically selects the optimal full-screen mode
  • Mouse input changes:
    • The mouse coordinates obtained by lstg.GetMousePosition are relative to the canvas
    • The mouse coordinates obtained by lstg.Input.Mouse.GetPosition are relative to the canvas
  • Renderer changes:
    • lstg.CreateRenderTarget creates an "auto-size" (do not fill in the size parameter) render target whose size is fixed to the size of the canvas
    • lstg.SetImageScale no longer supports modifying the global rendering scale (for compatibility, instead of throwing an error, print a warning) (keep consistency of API behavior)
    • lstg.Snapshot fixedly captures the content of the canvas

Progress:

• [x] Design
• [x] Development
• [x] Public test
• [x] Release and declare the feature as stable