Make hot corners configurable, including per-output (#2108)

* Add corner selection in config

* Add hot corner docs

* Working per-monitor hot corners

Handle defaults

* run cargo fmt --all

* Fix hot corners in is_sticky_obscured_under

* Change default to fall back to gesture hot corners if output hot corners are unset

* Add hot corner output config docs

* Support fractional scaling

* Trigger hot corners over widgets

* Improve float handling
Fixed YaLTeR/niri/pull/2108

* Refactor

* Bug Fixes

* Amend docs

Fix styling

Co-authored-by: Ivan Molodetskikh <yalterz@gmail.com>

* Integrate code review

Move is_inside_hot_corner

* fixes

---------

Co-authored-by: Aadniz <8147434+Aadniz@users.noreply.github.com>
Co-authored-by: Ivan Molodetskikh <yalterz@gmail.com>

docs/wiki/Configuration:-Gestures.md

@@ -23,6 +23,10 @@ gestures {
 
     hot-corners {
         // off
+        top-left
+        // top-right
+        // bottom-left
+        // bottom-right
     }
 }
 ```
@@ -94,3 +98,18 @@ gestures {
     }
 }
 ```
+
+<sup>Since: next release</sup> You can choose specific hot corners by name: `top-left`, `top-right`, `bottom-left`, `bottom-right`.
+If no corners are explicitly set, the top-left corner will be active by default.
+
+```kdl
+// Enable the top-right and bottom-right hot corners.
+gestures {
+    hot-corners {
+        top-right
+        bottom-right
+    }
+}
+```
+
+You can also customize hot corners per-output [in the output config](./Configuration:-Outputs.md#hot-corners).