This adds a feature counter for WASM shared memory (i.e. the presence
of the "shared" bit in a WASM module's memory section) and the usage
of WASM threads opcodes (i.e. wake/wait and atomics).

This CL also plumbs the WasmFeatures through the compilation pipeline
to detect features as functions are being compiled.

R=ahaas@chromium.org, ulan@chromium.org
BUG=chromium:868844

Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: I854f932d3adb16e4fd87196fe2a193950295b856
Reviewed-on: https://chromium-review.googlesource.com/1186329Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55337}