* Fix gather_op by adding OurOfRangeCheck for param[Index]

* Code Optimization

* fix gather shape bug

* fix None

* fix topo

test=develop

* fixed the code for coverage

* fixed the document,test=document_preview test=develop

* gather_op support int64_t index by adding a template typename

* add UT and rename typename

test=develop

test=develop

* Add int type support for stack_op

* Improve gather op to support index with shape N x 1

test=develop

* Fix stack_op kernel's registry

test=develop

Polish styles in generate_proposals_op.

1. inline lambda functions rathar than use std::function to save var.
2. add `static inline` to template functions .cc
   * Make them static to prevent generating symbols.
   * Make them inline to give compiler a hit inline them as possible.
   * Not if the function is not static, they cannot be inlined since the
     symbols should be exported.
3. add `static` to global functions in .cc
   * Make them static to prevent generating symbols.
4. Use Vector<uint64> instead manually manange storage between devices.
5. Prefer to use platform::ForRange, so we can optimize `ForRange` by
   just changing `for_range.h` if it is needed.
6. Do not change shape of inputs

test=develop

gather scatter gpu