JIT: Pass field's owner to getFieldType

[EgorBo]

Closes#96787

Also, removes the variance check from:

privatereadonlyList<string>_list=new(){"a","b","c"};[Benchmark]publicSpan<string>AsSpan()=>CollectionsMarshal.AsSpan(_list);

Codegen diff (Main vs PR): https://www.diffchecker.com/dZnlDi91/

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Issue Details

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Closes #96787

Also, removes the variance check from:

privatereadonlyList<string>_list=new(){"a","b","c"};[Benchmark]publicSpan<string>AsSpan()=>CollectionsMarshal.AsSpan(_list);

Codegen diff (Main vs PR): https://www.diffchecker.com/dZnlDi91/

Author:	EgorBo
Assignees:	-
Labels:	area-CodeGen-coreclr
Milestone:	-

[EgorBo]

@MihuBot

[EgorBo]

@MihuBot

[jkotas]

Existing related codegen bug: #96876

[EgorBo]

@MihuBot

[EgorBo]

@MihuBot

[ghost]

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