[wasm] Enable --wasm-opt

This CL enables basic optimizations in TurboFan for WebAssembly code,
like dead code elimination (DeadCodeElimination), constant folding
(MachineOperatorReducer), and control flow optimizations
(CommonOperatorReducer).

These optimizations were disabled originally to improve startup time,
at the expense of slower generated code. However, with Liftoff as the
baseline compiler, startup time is not so important anymore for
TurboFan.

R=clemensb@chromium.org
CC=manoskouk@chromium.org

Change-Id: I2a81f66929c43fbbdfc3625359772c8ea0f2235f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2488684Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70691}

src/flags/flag-definitions.h

@@ -864,7 +864,7 @@ DEFINE_BOOL(wasm_staging, false, "enable staged wasm features")
 FOREACH_WASM_STAGING_FEATURE_FLAG(WASM_STAGING_IMPLICATION)
 #undef WASM_STAGING_IMPLICATION
 
-DEFINE_BOOL(wasm_opt, false, "enable wasm optimization")
+DEFINE_BOOL(wasm_opt, true, "enable wasm optimization")
 DEFINE_BOOL(
     wasm_bounds_checks, true,
     "enable bounds checks (disable for performance testing only)")