Added CreateStruct & Fixed CreateMap

[cschuchardt88]

Description

• Added CreateStruct method
• CreateMap changed to initialize items on the stack to be packed as a new map. Changed to follow CreateArray and CreateStruct.
• Type case removed because in C# char already is a ushort.

Type of change

• Optimization (the change is only an optimization)
• Style (the change is only a code style for better maintenance or standard purpose)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

• Unit tests

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[Jim8y]

can you add a little bit more explanation on this pr.

[roman-khimov]

Changes are nice, but I don't like the way they're stuffed into a single commit without any real comments (more efficient packer is not a "fix", additional method is an additional method, type cast is a separate matter as well).

[cschuchardt88]

I updated the description in the 1st comment.

[Jim8y]

Value can not be null? Do we have this limitation before?

[cschuchardt88]

You can't do map[null] = null. You could before but wouldn't work. Needs to be StackItem.Null.

This just stop you from using value types from being null like byte?, int? and etc