optimizer: simple array SROA

Implements a simple Julia-level array allocation elimination on top of #43888.

```julia
julia> code_typed((String,String)) do s, t
           a = Vector{Base.RefValue{String}}(undef, 2)
           a[1] = Ref(s)
           a[2] = Ref(t)
           return a[1][]
       end
```
```diff
diff --git a/master b/pr
index 9c8da14380..5b63d08190 100644
--- a/master
+++ b/pr
@@ -1,11 +1,4 @@
 1-element Vector{Any}:
  CodeInfo(
-1 ─ %1 = $(Expr(:foreigncall, :(:jl_alloc_array_1d), Vector{Base.RefValue{String}}, svec(Any, Int64), 0, :(:ccall), Vector{Base.RefValue{String}}, 2, 2))::Vector{Base.RefValue{String}}
-│   %2 = %new(Base.RefValue{String}, s)::Base.RefValue{String}
-│        Base.arrayset(true, %1, %2, 1)::Vector{Base.RefValue{String}}
-│   %4 = %new(Base.RefValue{String}, t)::Base.RefValue{String}
-│        Base.arrayset(true, %1, %4, 2)::Vector{Base.RefValue{String}}
-│   %6 = Base.arrayref(true, %1, 1)::Base.RefValue{String}
-│   %7 = Base.getfield(%6, :x)::String
-└──      return %7
+1 ─     return s
 ) => String
```

Still this array SROA handle is very limited and able to handle only
trivial examples (though I confirmed this version already eliminates
few array allocations during sysimg build).
For those who interested, I added some discussions on array optimization
[here](https://aviatesk.github.io/EscapeAnalysis.jl/dev/#EA-Array-Analysis).

Author: aviatesk

base/compiler/optimize.jl

@@ -288,8 +288,7 @@ end
 
 function foreigncall_effect_free(stmt::Expr, src::Union{IRCode,IncrementalCompact})
     args = stmt.args
-    name = args[1]
-    isa(name, QuoteNode) && (name = name.value)
+    name = normalize(args[1])
     isa(name, Symbol) || return false
     ndims = alloc_array_ndims(name)
     if ndims !== nothing
@@ -315,6 +314,17 @@ function alloc_array_ndims(name::Symbol)
     return nothing
 end
 
+normalize(@nospecialize x) = isa(x, QuoteNode) ? x.value : x
+
+function is_array_alloc(@nospecialize stmt)
+    isa(stmt, Expr) || return false
+    if isexpr(stmt, :foreigncall)
+        name = normalize(stmt.args[1])
+        return isa(name, Symbol) && alloc_array_ndims(name) !== nothing
+    end
+    return false
+end
+
 const FOREIGNCALL_ARG_START = 6
 
 function alloc_array_no_throw(args::Vector{Any}, ndims::Int, src::Union{IRCode,IncrementalCompact})