Boa Gc implementation draft (#2394)

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Not sure if anyone else may be working on something more substantial/in-depth, but I thought I'd post this. 😄 

The basic rundown is that this is more of an untested (and in some ways naïve) draft than anything else. It builds rather heavily on `rust-gc`, and tries to keep plenty of the core aspects so as to not break anything too much, and also to minimize overarching changes were it to actually be merged at some point.

This implementation does add ~~a generational divide (although a little unoptimized) to the heap,~~ a GcAlloc/Collector struct with methods, and an ephemeron implementation that allows for the WeakPair and WeakGc pointers.

boa_engine/Cargo.toml

@@ -37,7 +37,6 @@ boa_profiler.workspace = true
 boa_macros.workspace = true
 boa_ast.workspace = true
 boa_parser.workspace = true
-gc = "0.4.1"
 serde = { version = "1.0.147", features = ["derive", "rc"] }
 serde_json = "1.0.87"
 rand = "0.8.5"