AArch64 Scalable vector debug info crash

See https://godbolt.org/z/9dKMr7vT6

```
target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
target triple = "aarch64-unknown-linux-gnu"

define @scalable_vector_debug_info( %arg) #0 !dbg !7 {
; CHECK-LABEL: scalable_vector_debug_info:
; CHECK: .Lfunc_begin0:
; CHECK-NEXT: .cfi_startproc
; CHECK-NEXT: // %bb.0:
; CHECK-NEXT: //DEBUG_VALUE: scalable_vector_debug_info:arg <- $z0
; CHECK-NEXT: ret
#dbg_value( %arg, !13, !DIExpression(), !14)
%extract = tail call @llvm.vector.extract.nxv8f16.nxv16f16( %arg, i64 0)
ret %arg
}

declare @llvm.vector.extract.nxv8f16.nxv16f16(, i64 immarg)

attributes #0 = { "aarch64_pstate_sm_enabled" "target-features"="+sme" }

!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!3, !4, !5, !6}

!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
!1 = !DIFile(filename: "scalable-vector-debug.c", directory: "/tmp")
!2 = !{}
!3 = !{i32 2, !"Dwarf Version", i32 4}
!4 = !{i32 2, !"Debug Info Version", i32 3}
!5 = !{i32 1, !"wchar_size", i32 4}
!6 = !{i32 7, !"frame-pointer", i32 2}
!7 = distinct !DISubprogram(name: "scalable_vector_debug_info", scope: !1, file: !1, line: 1, type: !8, scopeLine: 1, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !12)
!8 = !DISubroutineType(types: !9)
!9 = !{!10, !10}
!10 = !DIBasicType(name: "svfloat16_t", size: 16, encoding: DW_ATE_float)
!11 = !DIBasicType(name: "__fp16", size: 16, encoding: DW_ATE_float)
!12 = !{!13}
!13 = !DILocalVariable(name: "arg", arg: 1, scope: !7, file: !1, line: 1, type: !10)
!14 = !DILocation(line: 0, scope: !7)
!15 = distinct !DISubprogram(name: "streaming_sve_debug_info", scope: !1, file: !1, line: 5, type: !8, scopeLine: 5, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !18)
!16 = !DILocalVariable(name: "arg", arg: 1, scope: !15, file: !1, line: 5, type: !10)
!17 = !DILocation(line: 0, scope: !15)
!18 = !{!16}
```

Compiling with `llc -mtriple aarch64 -mattr=+sme` triggers:
`LLVM ERROR: Cannot implicitly convert a scalable size to a fixed-width size in TypeSize::operator ScalarTy()`

Start with the godbolt reproducer and run the shown llc -mtriple aarch64 -mattr=+sme command to reproduce the TypeSize conversion error. Trace the scalable-vector debug-info path around the reported failure, then verify that compilation completes and produces the expected CHECK debug output without the crash.

Written by the indexing model from the issue text.