C/JS accessors for function table segments

[bvibber]

module.getNumFunctionTableSegments() gives the number of segments.

module.getFunctionTableSegmentInfoByIndex() yields:

{
  offset,
  functions: ["func1", "func2"]
}

Another piece for #2370

[COFFEETALES]

Great stuff.
I have done a similar work at #2554
At least, we will definitively get something for the function table 👍

[bvibber]

Heh, didn't see yours... :) I like your version better, it has the import marker and can support non constant init I think?

[COFFEETALES]

Thanks, but you did well too.

In my version, the offset is treated as a regular wasm expression.
The user has to fetch the content with getExpressionInfo(segment.offset).
I think it's cleaner than trying to find out what lies behind the expression.

At some point, it could be relevant to use the same approach for getMemorySegmentInfoByIndex.
I don't know, just an idea...

[bvibber]

Closing in favor of #2554