* Add ReadOnly{Observable}Collection/Dictionary.Empty

* Revert XamlLoadPermission.cs change to fix downlevel build

* Eliminate temporary -1 on Socket.Unix.cs

repPrintObjectDescription was not null-terminating when the map was
null. There is SPMI error trap on the JIT side so we can just make it
fail on missing data.

repGetStringLiteral should not succeed on missing data, it is used for
optimization purposes.

…71971)" (#77360)

This reverts commit 8cb4e93.

Limit to cases where are actually performing replacements to mitigate TP impact.

- Add IMemoryView as exported type.
- IMemoryView extends IDisposable.

…rbid mismatched struct assignments (#76766)

* GenTree::GetLayout field FIELDs

* Do not create invalid IR when replacing promoted fields

Instead, create constructions like "OBJ(ADDR(LCL_VAR))"
that block morphing can recognize on its own.

* Delete lvFieldHnd

* GenTree::GetLayout - CALL/COMMA

* GenTreeHWIntrinsic::GetLayout

* Add an assert that LHS and RHS match

* Fix assert violation

And simplify the code...

* Delete RetypedAsScalarFieldsMap

Without handle equality, the assert no longer holds, for example:
```cs
private StructWithInt Problem(StructWithInt b, StructWithInt a)
{
    a = ((StructWithStructWithInt*)&b)->StructWithInt;
    return a;
}
```

* Delete a bit of code

Dead / unncessary.

No diffs.

* Fold promoted locals in local morph

* Support GT_IND in MorphStructField

This is significantly simpler than moving the promotion logic
to post-order because we don't need to fiddle with the ref
counting process and complexities of intermediate states, e. g.
"IND<float>(ADDR(FIELD<int>(ADDR(LCL_VAR<struct>))))" can be
naturally turned into "BITCAST<float>(LCL_VAR<int>)" like this.

* More code removal

* Move "fgMorphStructField" to local morph

* TP tuning

With this, we have only a very small regression:

Base: 1297463478, Diff: 1297750893, +0.0222%
LocalAddressVisitor::MorphStructField : 345099  : NA       : 31.52% : +0.0266%
LocalAddressVisitor::PreOrderVisit    : 224684  : +3.53%   : 20.52% : +0.0173%
memset                                : 88591   : +0.99%   : 8.09%  : +0.0068%
Compiler::fgMorphSmpOp                : -19170  : -0.06%   : 1.75%  : -0.0015%
Compiler::fgMorphStructField          : -367474 : -100.00% : 33.56% : -0.0283%

(This is with a dummy field on LclVarDsc)

Losing the assert does not seem worrysome as we have an identical one in "fgMorphField".

System.Private.CoreLib, System.Threading.Tasks.Dataflow, and System.Threading.Channels have all ended up with their own copy of SingleProducerSingleConsumerQueue and its associated helpers.  This consolidates them down to a single shared copy.

There's no functional change here, just deleting duplicates and moving things around.

* Fix #77212.

* Remove unneeded using statement.

This enhances parts of the SPMI process with more information on failures.

Also fixes a bug I introduced when I added tpdiffs: when asmdiffs fails, it was not marking the entire pipeline as failing.

* Consolidate the GUID to string logic

Replace obvious uses of GUID to string
logic with a new constant for buffer length.