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:-Outputs.md

@@ -16,6 +16,14 @@ output "eDP-1" {
     focus-at-startup
     background-color "#003300"
     backdrop-color "#001100"
+
+    hot-corners {
+        // off
+        top-left
+        // top-right
+        // bottom-left
+        // bottom-right
+    }
 }
 
 output "HDMI-A-1" {
@@ -217,3 +225,31 @@ output "HDMI-A-1" {
     backdrop-color "#001100"
 }
 ```
+
+### `hot-corners`
+
+<sup>Since: next release</sup>
+
+Customize the hot corners for this output.
+By default, hot corners [in the gestures settings](./Configuration:-Gestures.md#hot-corners) are used for all outputs.
+
+Hot corners toggle the overview when you put your mouse at the very corner of a monitor.
+
+`off` will disable the hot corners on this output, and writing specific corners will enable only those hot corners on this output.
+
+```kdl
+// Enable the bottom-left and bottom-right hot corners on HDMI-A-1.
+output "HDMI-A-1" {
+    hot-corners {
+        bottom-left
+        bottom-right
+    }
+}
+
+// Disable the hot corners on DP-2.
+output "DP-2" {
+    hot-corners {
+        off
+    }
+}
+```