Auto merge of #105446 - erikdesjardins:vt-size, r=nikic

Add 0..=isize::MAX range metadata to size loads from vtables

This is the (much belated) size counterpart to #91569.

Inspired by https://rust-lang.zulipchat.com/#narrow/stream/187780-t-compiler.2Fwg-llvm/topic/Range.20metadata.20for.20.60size_of_val.60.20and.20other.20isize.3A.3AMAX.20limits. This could help optimize layout computations based on the size of a dyn trait. Though, admittedly, adding this to vtables wouldn't be as beneficial as adding it to slice len, which is used much more often.

Miri detects this UB already: https://github.com/rust-lang/rust/blob/b7cc99142ad0cfe47e2fe9f7a82eaf5b672c0573/compiler/rustc_const_eval/src/interpret/traits.rs#L119-L121
(In fact Miri goes further, [assuming a 48-bit address space on 64-bit platforms](https://github.com/rust-lang/rust/blob/9db224fc908059986c179fc6ec433944e9cfce50/compiler/rustc_abi/src/lib.rs#L312-L331), but I don't think we can assume that in an optimization.)

Author: bors