Ladybird: Move helper processes to CMAKE_INSTALL_LIBEXECDIR

It aligns better with the Filesystem Heirarchy Standard[1] to put our
program-specific helper programs that are not intended to be executed by
the user of the application in $prefix/libexec or in whatever the
packager sets as the CMake equivalent. Namely, on Debian systems this
should be /usr/lib/Ladybird or similar.

[1] https://refspecs.linuxfoundation.org/FHS_3.0/fhs-3.0.html#usrlibexec

Meta/gn/secondary/Ladybird/BUILD.gn

@@ -181,6 +181,7 @@ executable("headless-browser") {
     "HelperProcess.cpp",
     "Utilities.cpp",
   ]
+  output_dir = "$root_out_dir/libexec"
 }
 
 fonts = [

Meta/gn/secondary/Ladybird/ImageDecoder/BUILD.gn

@@ -16,4 +16,5 @@ executable("ImageDecoder") {
     "//Userland/Services/ImageDecoder/ConnectionFromClient.cpp",
     "main.cpp",
   ]
+  output_dir = "$root_out_dir/libexec"
 }

Meta/gn/secondary/Ladybird/RequestServer/BUILD.gn

@@ -29,4 +29,5 @@ executable("RequestServer") {
     "//Userland/Services/RequestServer/Request.cpp",
     "main.cpp",
   ]
+  output_dir = "$root_out_dir/libexec"
 }

Meta/gn/secondary/Ladybird/SQLServer/BUILD.gn

@@ -17,4 +17,5 @@ executable("SQLServer") {
     "//Userland/Services/SQLServer/SQLStatement.cpp",
     "main.cpp",
   ]
+  output_dir = "$root_out_dir/libexec"
 }

Meta/gn/secondary/Ladybird/WebContent/BUILD.gn

@@ -81,4 +81,5 @@ executable("WebContent") {
     cflags_cc = [ "-DHAS_ACCELERATED_GRAPHICS" ]
     deps += [ "//Userland/Libraries/LibAccelGfx" ]
   }
+  output_dir = "$root_out_dir/libexec"
 }

Meta/gn/secondary/Ladybird/WebDriver/BUILD.gn

@@ -27,4 +27,5 @@ executable("WebDriver") {
     "//Userland/Services/WebDriver/WebContentConnection.cpp",
     "main.cpp",
   ]
+  output_dir = "$root_out_dir/libexec"
 }

Meta/gn/secondary/Ladybird/WebSocket/BUILD.gn

@@ -18,4 +18,5 @@ executable("WebSocket") {
     "//Userland/Services/WebSocket/ConnectionFromClient.cpp",
     "main.cpp",
   ]
+  output_dir = "$root_out_dir/libexec"
 }

Meta/gn/secondary/Ladybird/WebWorker/BUILD.gn

@@ -28,4 +28,5 @@ executable("WebWorker") {
     "//Userland/Services/WebWorker/PageHost.cpp",
     "main.cpp",
   ]
+  output_dir = "$root_out_dir/libexec"
 }