Scalarize single-field-to-lclVar block copy
Scalarize single-field-to-lclVar block copy

Morph has some logic to scalarize struct copies where the RHS is a scalar
and the LHS is a single-field struct.  This change adds the symmetric
logic where the LHS is a scalar and the RHS is a single-field struct.
This pattern shows up in Span<T> methods that initialize the data pointer
field, due to the way scalar replacement operates on spans.

mskvortsov/coreclr,alexperovich/coreclr,mskvortsov/coreclr,ragmani/coreclr,gkhanna79/coreclr,AlexGhiondea/coreclr,poizan42/coreclr,wateret/coreclr,dpodder/coreclr,jamesqo/coreclr,wtgodbe/coreclr,yeaicc/coreclr,krytarowski/coreclr,ragmani/coreclr,sagood/coreclr,krytarowski/coreclr,gkhanna79/coreclr,tijoytom/coreclr,qiudesong/coreclr,AlexGhiondea/coreclr,pgavlin/coreclr,James-Ko/coreclr,JosephTremoulet/coreclr,JonHanna/coreclr,krytarowski/coreclr,qiudesong/coreclr,wateret/coreclr,James-Ko/coreclr,tijoytom/coreclr,YongseopKim/coreclr,kyulee1/coreclr,jamesqo/coreclr,ragmani/coreclr,parjong/coreclr,cydhaselton/coreclr,AlexGhiondea/coreclr,krytarowski/coreclr,ragmani/coreclr,russellhadley/coreclr,JosephTremoulet/coreclr,poizan42/coreclr,cmckinsey/coreclr,alexperovich/coreclr,botaberg/coreclr,wtgodbe/coreclr,krytarowski/coreclr,yizhang82/coreclr,JosephTremoulet/coreclr,botaberg/coreclr,mskvortsov/coreclr,JosephTremoulet/coreclr,hseok-oh/coreclr,pgavlin/coreclr,poizan42/coreclr,yizhang82/coreclr,cshung/coreclr,mskvortsov/coreclr,wtgodbe/coreclr,dpodder/coreclr,parjong/coreclr,kyulee1/coreclr,rartemev/coreclr,cydhaselton/coreclr,JonHanna/coreclr,tijoytom/coreclr,dpodder/coreclr,YongseopKim/coreclr,mskvortsov/coreclr,ruben-ayrapetyan/coreclr,dpodder/coreclr,cshung/coreclr,qiudesong/coreclr,cmckinsey/coreclr,botaberg/coreclr,rartemev/coreclr,krk/coreclr,sagood/coreclr,krk/coreclr,alexperovich/coreclr,gkhanna79/coreclr,yizhang82/coreclr,cydhaselton/coreclr,rartemev/coreclr,mmitche/coreclr,yizhang82/coreclr,botaberg/coreclr,yeaicc/coreclr,mmitche/coreclr,hseok-oh/coreclr,JonHanna/coreclr,rartemev/coreclr,tijoytom/coreclr,AlexGhiondea/coreclr,cydhaselton/coreclr,cmckinsey/coreclr,pgavlin/coreclr,krk/coreclr,parjong/coreclr,wateret/coreclr,russellhadley/coreclr,yeaicc/coreclr,russellhadley/coreclr,pgavlin/coreclr,qiudesong/coreclr,russellhadley/coreclr,russellhadley/coreclr,JonHanna/coreclr,wtgodbe/coreclr,kyulee1/coreclr,cshung/coreclr,ragmani/coreclr,ruben-ayrapetyan/coreclr,ruben-ayrapetyan/coreclr,pgavlin/coreclr,James-Ko/coreclr,cmckinsey/coreclr,poizan42/coreclr,AlexGhiondea/coreclr,wtgodbe/coreclr,parjong/coreclr,qiudesong/coreclr,ruben-ayrapetyan/coreclr,JosephTremoulet/coreclr,hseok-oh/coreclr,hseok-oh/coreclr,James-Ko/coreclr,hseok-oh/coreclr,James-Ko/coreclr,sagood/coreclr,sagood/coreclr,yeaicc/coreclr,YongseopKim/coreclr,wateret/coreclr,jamesqo/coreclr,sagood/coreclr,pgavlin/coreclr,botaberg/coreclr,James-Ko/coreclr,cmckinsey/coreclr,yizhang82/coreclr,krk/coreclr,YongseopKim/coreclr,mmitche/coreclr,poizan42/coreclr,ragmani/coreclr,alexperovich/coreclr,jamesqo/coreclr,parjong/coreclr,jamesqo/coreclr,cmckinsey/coreclr,rartemev/coreclr,hseok-oh/coreclr,wtgodbe/coreclr,AlexGhiondea/coreclr,mmitche/coreclr,YongseopKim/coreclr,gkhanna79/coreclr,jamesqo/coreclr,russellhadley/coreclr,ruben-ayrapetyan/coreclr,wateret/coreclr,krk/coreclr,yeaicc/coreclr,cshung/coreclr,kyulee1/coreclr,cydhaselton/coreclr,kyulee1/coreclr,JonHanna/coreclr,mmitche/coreclr,poizan42/coreclr,rartemev/coreclr,tijoytom/coreclr,sagood/coreclr,yizhang82/coreclr,tijoytom/coreclr,dpodder/coreclr,krk/coreclr,gkhanna79/coreclr,mskvortsov/coreclr,cshung/coreclr,JosephTremoulet/coreclr,krytarowski/coreclr,JonHanna/coreclr,kyulee1/coreclr,alexperovich/coreclr,alexperovich/coreclr,cydhaselton/coreclr,cshung/coreclr,ruben-ayrapetyan/coreclr,YongseopKim/coreclr,botaberg/coreclr,dpodder/coreclr,yeaicc/coreclr,gkhanna79/coreclr,mmitche/coreclr,qiudesong/coreclr,yeaicc/coreclr,wateret/coreclr,parjong/coreclr,cmckinsey/coreclr