Add support for the custom-page-sizes proposal

[keithw]

This PR adds support for the custom-page-sizes proposal to the lexer, the binary/text parsers and writers, the validator, interpreter, and objdump.

Will plan to add wasm2c in a future PR.

(@fitzgen)

[sbc100]

Nice!

[fitzgen]

Very cool! Love to see it! I'll add a link to this PR from the proposal's Overview.md.

[fitzgen]

FWIW, if you want to hammer on this implementation a bit, wasm-smith has support for generating pseudorandom Wasm modules that use the custom-page-sizes proposal and you can use it via the CLI as well if you don't want to link to Rust code:

$ head -n 100 < /dev/urandom | wasm-tools smith -t --custom-page-sizes-enabled=true --max-memories=20
(module
  (table (;0;) 567 296841 externref)
  (memory (;0;) i64 345681 (pagesize 0x1))
  (global (;0;) f64 f64.const -0x1.cbe613cfc1799p+665 (;=-275023225219671150000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000;))
  (global (;1;) externref ref.null extern)
  (export "" (table 0))
  (export "\u{1d}k1" (table 0))
  (elem (;0;) declare funcref)
  (data (;0;) "")
)

You can throw that in a loop, pass each test case to WABT, and see if you can find any bugs :)

(There are also lots of other knobs you can configure to control Wasm module generation, for example you can disable random imports to make the modules self contained, turn off the GC proposal, etc...)