Add `matches` function to all types structs

[BoilingFusion]

Feature

Currently there exist FuncType::matches and ValType::matches.

Add matches functions to:

• ExternType
• GlobalType
• TableType
• TagType

Benefit

Quickly checking if a type conforms to an interface.
Asking this in relation to this wasmi pull request to know if there are any plans on implementing functions like this.

Implementation

I think it should be possible to compare all fields for either equality or to use the matches functions that are already written.

Alternatives

These functions do not have to be written in this crate. They can also be added by users of the library if necessary.

[alexcrichton]

Seems reasonable to me to add yeah, happy to review PRs!