Using custom ceilf inline impl in ImGui::CalcTextSize().

Amend 7b0bf230, 4622fa4b6, 12b7977. (#791)

imgui.cpp

diff --git a/imgui.cpp b/imgui.cpp
index 735deb9..28fc2aa 100644
--- a/imgui.cpp
+++ b/imgui.cpp
@@ -6199,10 +6199,9 @@
     ImVec2 text_size = font->CalcTextSizeA(font_size, FLT_MAX, wrap_width, text, text_display_end, NULL);
 
     // Round
-    // FIXME: This has been here since Dec 2015 (7b0bf230 then 4622fa4b6) but down the line we want this out. See #791.
-    // Investigate using ceilf or e.g. https://git.musl-libc.org/cgit/musl/tree/src/math/ceilf.c, https://embarkstudios.github.io/rust-gpu/api/src/libm/math/ceilf.rs.html
-    // The problem is that ceilf() has a measurable cost. Not high, but measurable!
-    text_size.x = IM_TRUNC(text_size.x + 0.999f);
+    // (see 7b0bf230, 4622fa4b6, #791 for details about this.)
+    // FIXME: Add a way to disable this.
+    text_size.x = ImCeilFast(text_size.x);
 
     return text_size;
 }

imgui.h

diff --git a/imgui.h b/imgui.h
index cc80fc8..2aa8cb0 100644
--- a/imgui.h
+++ b/imgui.h
@@ -30,7 +30,7 @@
 // Library Version
 // (Integer encoded as XYYZZ for use in #if preprocessor conditionals, e.g. '#if IMGUI_VERSION_NUM >= 12345')
 #define IMGUI_VERSION       "1.92.9 WIP"
-#define IMGUI_VERSION_NUM   19281
+#define IMGUI_VERSION_NUM   19282
 #define IMGUI_HAS_TABLE             // Added BeginTable() - from IMGUI_VERSION_NUM >= 18000
 #define IMGUI_HAS_TEXTURES          // Added ImGuiBackendFlags_RendererHasTextures - from IMGUI_VERSION_NUM >= 19198
 

imgui_internal.h

diff --git a/imgui_internal.h b/imgui_internal.h
index 70f2bad..4b9e18d 100644
--- a/imgui_internal.h
+++ b/imgui_internal.h
@@ -531,6 +531,7 @@
 inline ImVec2 ImFloor(const ImVec2& v)                                  { return ImVec2(ImFloor(v.x), ImFloor(v.y)); }
 inline float  ImTrunc64(float f)                                        { return (float)(ImS64)(f); }
 inline float  ImRound64(float f)                                        { return (float)(ImS64)(f + 0.5f); } // FIXME: Positive values only.
+inline float  ImCeilFast(float f)                                       { int i = (int)f; return (float)(i + (f > (float)i)); } // Consider using the the bit-hack version (search for "0x1p120f").
 inline int    ImModPositive(int a, int b)                               { return (a + b) % b; }
 inline float  ImDot(const ImVec2& a, const ImVec2& b)                   { return a.x * b.x + a.y * b.y; }
 inline ImVec2 ImRotate(const ImVec2& v, float cos_a, float sin_a)       { return ImVec2(v.x * cos_a - v.y * sin_a, v.x * sin_a + v.y * cos_a); }