JIT: revisions to struct field escape analysis (#116124)

* JIT: revisions to struct field escape analysis

Peel off some changes from the more general field-wise escape analysis:
* make sure we have modelled all relevant stores. Change local store tracking to use the new model.
* keep track of which temps will represent stack allocated arrays and do suitable retyping
* reject "known escaping" allocations earlier (eg finalizable objects)
* handle local fields (rare but can exist in importer IR)
* add the field test cases; all of these stack allocate for now
* keep retyping layouts after first indir; add test

Author: AndyAyersMS

src/coreclr/jit/gentree.h

@@ -450,7 +450,6 @@ enum GenTreeFlags : unsigned int
     GTF_VAR_MOREUSES      = 0x00800000, // GT_LCL_VAR -- this node has additional uses, for example due to cloning
     GTF_VAR_CONTEXT       = 0x00400000, // GT_LCL_VAR -- this node is part of a runtime lookup
     GTF_VAR_EXPLICIT_INIT = 0x00200000, // GT_LCL_VAR -- this node is an "explicit init" store. Valid until rationalization.
-    GTF_VAR_CONNECTED     = 0x00100000, // GT_STORE_LCL_VAR -- this store was modelled in the connection graph during escape analysis
 
     // For additional flags for GT_CALL node see GTF_CALL_M_*