Update description of input parameter type and return type limitations

[minaminao]

ABI coder V2 is now enabled by default. It allows us to do the following:

• Multidimensional arrays (including dynamic arrays) can be used as input for external functions.
• Multidimensional arrays (including dynamic arrays) and structs can be used as return values for external functions.

I changed the documentation based on this. (I have already experimented on my machine to make sure it works.)

However, mapping is not allowed as a return value before, so I left it as it is.

EDIT: I am not aware whether all multidimensional arrays of all value types are supported by ABI coder V2.

[cameel]

The failing OpenZeppelin test is already fixed on latest develop. I rebased the PR and pushed to the original branch to make it pass so that we can merge this.

I also added some more tweaks while at it:

• Expanded the note according to @ekpyron's comment but with even more detail
• Removed another mention of v2 not being the default
• Added more consistent index entries for pragmas.

@minaminao Please check if you're fine with these changes.

[minaminao]

Looks good. It's helpful to clearly understand the specifications.

[leonardoalt]

Rebased and applied suggestions from @ekpyron .