Merge with extra: opencv/opencv_extra#865
Fixes #18214:

• issue 1: aligned OCV and TF multiplication layer behaviour for the following case: inputs a (shape: [1,1,1, C] ) and b (shape: [1, H, W, C] ), OCV a mul b returns [1,1,1, C], whereas TF mul - [1, H, W, C].
• issue 2: MobileNetV3 reshape problem (before Conv layer): number of input channels should be multiple of 72 but got 1 in getMemoryShapes()

• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or other license that is incompatible with OpenCV
• The PR is proposed to proper branch
• There is reference to 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

force_builders=Custom,Custom Win,Custom Mac
build_image:Custom=ubuntu-openvino-2021.2.0:20.04
build_image:Custom Win=openvino-2021.1.0
build_image:Custom Mac=openvino-2021.2.0

test_modules:Custom=dnn,python2,python3,java
test_modules:Custom Win=dnn,python2,python3,java
test_modules:Custom Mac=dnn,python2,python3,java

buildworker:Custom=linux-1
# disabled due high memory usage: test_opencl:Custom=ON
test_opencl:Custom=OFF
test_bigdata:Custom=1
test_filter:Custom=*

allow_multiple_commits=1