Migrated to Godot 4

• Fixed syntax errors in GDScript and GLSL code subsequent to the migration from Godot 3 to 4
• Fixed uninitialized variable in camera lense shader causing the entire viewport to flicker
• Fixed banding in ocean shader due to gradient texture having swapped UVs in Godot 4
• Migrated the viewport-based flow map generator to a compute shader
• Fixed compatibility issues with Reverse-z in the ocean visual shader
• Fixed GLSL's smoothstep() usages where edge0 > edge1 which is undefined behavior in Vulkan
• Fixed various artifacts in ocean visual shader (among others : changes in linear / sRGB conversions, remove usage of fract() for UV coordinates causing texture filtering glitches, light() function not writing specular light to SPECULAR_LIGHT)
• Improved shaders' code readability by simplifying some expressions