The existing implementation causes unnecessary heap allocations for
javascript syscalls: Call, Invoke, and New. The new change seeks to
hint the Go compiler to allocate arg slices with length <=16 to the
stack.

Original Work: CL 367045
- Calling a JavaScript function with 16 arguments or fewer will not
induce two additional heap allocations, at least with the current Go
compiler.
- Using syscall/js features with slices and strings of
statically-known length will not cause them to be escaped to the heap,
at least with the current Go compiler.
- The reduction in allocations has the additional benefit that the
garbage collector runs less often, blocking WebAssembly's one and only
thread less often.

Fixes #39740

Change-Id: I815047e1d4f8ada796318e2064d38d3e63f73098
GitHub-Last-Rev: 36df1b33a4506e216767d8a73395f2fafdd80eba
GitHub-Pull-Request: golang/go#66684
Reviewed-on: https://go-review.googlesource.com/c/go/+/576575


Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>