ImVec2: Added unary minus operator (#6368)

Author: Koostosh

docs/CHANGELOG.txt

@@ -52,6 +52,7 @@ Other changes:
   erroneously initializing default nav layer to menu layer.
 - Menus: Fixed an issue when opening a menu hierarchy in a given menu-bar would allow
   opening another via simple hovering. (#3496, #4797)
+- Misc: Added ImVec2 unary minus operator. (#6368) [@Koostosh]
 - Debug Tools: Debug Log: Fixed not parsing 0xXXXXXXXX values for geo-locating on mouse
   hover hover when the identifier is at the end of the line. (#5855)
 - Backends: Clear bits sets io.BackendFlags on backend Shutdown(). (#6334, #6335] [@GereonV]

imgui.h

@@ -2352,7 +2352,6 @@ struct ImGuiListClipper
 // - It is important that we are keeping those disabled by default so they don't leak in user space.
 // - This is in order to allow user enabling implicit cast operators between ImVec2/ImVec4 and their own types (using IM_VEC2_CLASS_EXTRA in imconfig.h)
 // - You can use '#define IMGUI_DEFINE_MATH_OPERATORS' to import our operators, provided as a courtesy.
-// - We unfortunately don't have a unary- operator for ImVec2 because this would needs to be defined inside the class itself.
 #ifdef IMGUI_DEFINE_MATH_OPERATORS
 #define IMGUI_DEFINE_MATH_OPERATORS_IMPLEMENTED
 IM_MSVC_RUNTIME_CHECKS_OFF
@@ -2362,6 +2361,7 @@ static inline ImVec2  operator+(const ImVec2& lhs, const ImVec2& rhs)   { return
 static inline ImVec2  operator-(const ImVec2& lhs, const ImVec2& rhs)   { return ImVec2(lhs.x - rhs.x, lhs.y - rhs.y); }
 static inline ImVec2  operator*(const ImVec2& lhs, const ImVec2& rhs)   { return ImVec2(lhs.x * rhs.x, lhs.y * rhs.y); }
 static inline ImVec2  operator/(const ImVec2& lhs, const ImVec2& rhs)   { return ImVec2(lhs.x / rhs.x, lhs.y / rhs.y); }
+static inline ImVec2  operator-(const ImVec2& lhs)                      { return ImVec2(-lhs.x, -lhs.y); }
 static inline ImVec2& operator*=(ImVec2& lhs, const float rhs)          { lhs.x *= rhs; lhs.y *= rhs; return lhs; }
 static inline ImVec2& operator/=(ImVec2& lhs, const float rhs)          { lhs.x /= rhs; lhs.y /= rhs; return lhs; }
 static inline ImVec2& operator+=(ImVec2& lhs, const ImVec2& rhs)        { lhs.x += rhs.x; lhs.y += rhs.y; return lhs; }