Miscellaneous Meta.partially_inline! fixes (#56813)

This fixes up a couple of conspicuous problems I noticed when reviewing

I'm unsure we should have accepted this pass in Base to begin with... It
should at least be re-written to error on unexpected IR elements
(instead of performing an invalid transform silently), but the real
problem is that this pass is out-of-pipeline and so it doesn't run on
most user code and we have much worse coverage compared to passes in the
main Compiler.

(cherry picked from commit c1db3a4)

Author: topolarity

base/meta.jl

@@ -364,6 +364,19 @@ function _partially_inline!(@nospecialize(x), slot_replacements::Vector{Any},
         x.edges .+= slot_offset
         return x
     end
+    if isa(x, Core.UpsilonNode)
+        if !isdefined(x, :val)
+            return x
+        end
+        return Core.UpsilonNode(
+            _partially_inline!(x.val, slot_replacements, type_signature, static_param_values,
+                               slot_offset, statement_offset, boundscheck),
+        )
+    end
+    if isa(x, Core.PhiCNode)
+        _partially_inline!(x.values, slot_replacements, type_signature, static_param_values,
+                           slot_offset, statement_offset, boundscheck)
+    end
     if isa(x, Core.ReturnNode)
        # Unreachable doesn't have val defined
        if !isdefined(x, :val)