WasmBinaryReader: Consistent internal naming

[sbc100]

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For defined functions/globals/tables/memories use f1, t2, m3 etc.

This matches the longer names used for imports such as fimport$1, but keeps the names nice and short by avoiding the embedded dollar sign.

[sbc100]

Suspending work on this until https://github.com/WebAssembly/binaryen/pull/6813 lands

[sbc100]

I'm curious what you think of the general direction here? Are these names important? Should the be short? Should they be only numbers in some cases or should we always use some kind of type prefix?

[tlively]

I think that short names with disambiguating prefixes sound useful 👍