imgcodecs: Add rgb flag for imread and imdecode #25809
Try to `imread` images by RGB to save R-B swapping costs.
## How to use it?
```
img_rgb = cv2.imread("PATH", IMREAD_COLOR_RGB) # OpenCV decode the image by RGB format.
```
## TODO
- [x] Fix the broken code
- [x] Add imread rgb test
- [x] Speed test of rgb mode.
## Performance test
| file name | IMREAD_COLOR | IMREAD_COLOR_RGB |
| --------- | ------ | --------- |
| jpg01 | 284 ms | 277 ms |
| jpg02 | 376 ms | 366 ms |
| png01 | 62 ms | 60 ms |
| Png02 | 97 ms | 94 ms |
Test with [image_test.zip](https://github.com/user-attachments/files/15982949/image_test.zip)
```.cpp
string img_path = "/Users/mzh/work/data/image_test/png02.png";
int loop = 20;
TickMeter t;
double t0 = 10000;
for (int i = 0; i < loop; i++)
{
t.reset();
t.start();
img_bgr = imread(img_path, IMREAD_COLOR);
t.stop();
if (t.getTimeMilli() < t0) t0 = t.getTimeMilli();
}
std::cout<<"bgr time = "<<t0<<std::endl;
t0 = 10000;
for (int i = 0; i < loop; i++)
{
t.reset();
t.start();
img_rgb = imread(img_path, IMREAD_COLOR_RGB);
t.stop();
if (t.getTimeMilli() < t0) t0 = t.getTimeMilli();
}
std::cout<<"rgb time = "<<t0<<std::endl;
```
### Pull Request Readiness Checklist
See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request
- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [ ] There is a reference to the original bug report and related work
- [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
Patch to opencv_extra has the same branch name.
- [ ] The feature is well documented and sample code can be built with the project CMake
