Bump external/imgui from `b4c9635` to `22503bf` #1941

Job	Run time
clang-tidy	45s
cmake-lint	27s
cppcheck	50s
Codacy Security Scan	3m 59s
code-ql (cpp, gcc-14)	2m 38s
include-what-you-use	32s
DevSkim	30s
msvc-code-analysis (RelWithDebInfo)	4m 37s
ShellCheck	11s
	14m 29s

Provide feedback