Add OpenGL 4.6 backend for NanoVG

This commit introduces a new header file `nanovg_gl46.h` that implements
the NanoVG rendering context using OpenGL 4.6. The new backend utilizes
Direct State Access (DSA) functions, immutable texture storage, and
explicit layout qualifiers. It includes definitions for creating and
deleting the rendering context, as well as functions for handling images
with OpenGL 4.6.

samples/test.lua

@@ -1,5 +1,11 @@
 effect = nil
 video = nil
+ctx = nil
+
+timeDisplayText = ""
+dateDisplayText = ""
+
+timer = 0.0
 
 function _create()
     video = Texture.FromGStreamer("filesrc location=" .. Resolve("video.mkv"))
@@ -21,10 +27,28 @@ function _create()
         }
     ]]
     effect = Effect.new(fxSrc)
+
+    ctx = GraphicsContext.new()
+
+    local fontPath = Resolve("font.otf")
+    ctx:CreateFont("font", fontPath)
+
+    UpdateTimeAndDate()
+end
+
+function UpdateTimeAndDate()
+    local now = os.date("*t")
+    timeDisplayText = string.format("%02d:%02d", now.hour, now.min)
+    dateDisplayText = os.date("%A, %B %d, %Y")
 end
 
 function _update(dt)
+    timer = timer + dt
 
+    if timer >= 0.5 then
+        timer = 0.0
+        UpdateTimeAndDate()
+    end
 end
 
 function _render()
@@ -32,4 +56,23 @@ function _render()
     effect:Use()
     effect:SetTexture("uTexture", video, 0)
     effect:Render()
+
+    ctx:BeginFrame(DesktopSize.x, DesktopSize.y, DesktopSize.x / DesktopSize.y)
+
+    local xPos = 80.0
+    local yPos = 120.0
+    local timeFontSize = 80
+    local dateFontSize = 28
+
+    ctx:FontSize(timeFontSize)
+    ctx:FontFace("font")
+    ctx:FillColor(RGBAf(1, 1, 1, 0.75))
+    ctx:TextAlign(Align.RIGHT | Align.BOTTOM)
+    ctx:Text(Displays[1].x + Displays[1].z - xPos, Displays[1].y + Displays[1].w - yPos, timeDisplayText)
+
+    ctx:FontSize(dateFontSize)
+    ctx:FillColor(RGBAf(1, 1, 1, 0.45))
+    ctx:Text(Displays[1].x + Displays[1].z - xPos, Displays[1].y + Displays[1].w - (yPos + timeFontSize + 8), dateDisplayText)
+
+    ctx:EndFrame()
 end