[wasm] stop using mmap/munmap

[pavelsavara]

Contributes to #108510
Fixes #107215

Context

• sgen GC is using mono_valloc -> mmap on all other platforms.
• mmap emulator in emscripten and wasi-libc doens't implement partial munmap
  • It's implemented on top of malloc rather than on top of sbrk.
  • It has large alignment overhead and no added value.
• We have our own implementation of custom mmap
  • which can do partial munmap
  • but it never releases pages back to malloc pool.
• wasm could only grow, we can't return pages to OS/browser
• wasm32 adress space is rather small and could get fragmented easily

Changes

• set MS_BLOCK_ALLOC_NUM to 1 which prevents sgen from doing partial mono_vfree
• set LOCK_FREE_ALLOC_SB_MAX_SIZE to 16384 * 32 to compensate for above
• sgen_los_memory_usage_total is accounting for alignment
• implement mono_vfree using dlfree
• implement mono_valloc_aligned and mono_valloc using posix_memalign
  • emscripten sys_alloc implementation will stitch last segment to new memory allocated via sbrk
• avoids emscripten mmap which always calls memset to zero the memory
  • this PR brings optimization that new pages which are received from sbrk don't need that.
  • also some calls to mono_valloc pass MONO_MMAP_NOZERO
• removes mono-wasm-pagemgr.c and wasm-mmap option

TODO

• measure startup performance

[pavelsavara]

@radekdoulik could you please run startup benchmark on this PR ? Many thanks

[radekdoulik]

there are visible regressions in json on firefox. I will schedule the updated commit to have another measurement at hand

[radekdoulik]

the commit 5070e99 is measured and visible in the perf tool

[pavelsavara]

/ba-g all CI issues are known