src: always compile and store code cache for native modules

src: remove code cache integrity check

In preparation of sharing code cache among different threads - we simply rely on v8 to reject invalid cache, since there isn't any serious consequence when the cache is invalid anyway.

src: always compile and store code cache for native modules

This patch changes the NativeModuleLoader to always try to find code cache for native modules when it compiles them, and always produce and store the code cache after compilation. The cache map is protected by a mutex and can be accessed by different threads - including the worker threads and the main thread. Hence any thread can reuse the code cache if the native module has already been compiled by another thread - in particular the cache of the bootstrappers and per_context.js will always be hit when a new thread is spun.

This results in a ~6% startup overhead in the worst case (when only the main thread is launched without requiring any additional native module - it now needs to do the extra work of finding and storing caches), which balances out the recent improvements by moving the compilation to C++, but it also leads to a ~60% improvement in the best case (when a worker thread is spun and requires a lot of native modules thus hitting the cache compiled by the main thread).

Local benchmark results:

                                                                                   confidence improvement accuracy (*)   (**)  (***)
 misc/startup.js mode='process' script='benchmark/fixtures/require-cachable' dur=1        ***     -6.80 %       ±0.77% ±1.02% ±1.34%
 misc/startup.js mode='process' script='test/fixtures/semicolon' dur=1                    ***     -4.90 %       ±0.82% ±1.10% ±1.43%
 misc/startup.js mode='worker' script='benchmark/fixtures/require-cachable' dur=1         ***     63.13 %       ±1.58% ±2.12% ±2.79%
 misc/startup.js mode='worker' script='test/fixtures/semicolon' dur=1                     ***     56.20 %       ±1.33% ±1.78% ±2.33%

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines