Auto merge of rust-lang#74821 - oli-obk:const_eval_read_uninit_fast_path, r=wesleywiser

Check whether locals are too large instead of whether accesses into them are too large

Essentially this stops const prop from attempting to optimize

```rust
let mut x = [0_u8; 5000];
x[42] = 3;
```

I don't expect this to be a perf improvement without rust-lang#73656 (which is also where the lack of this PR will be a perf regression).

r? @wesleywiser

Author: bors

tests/ui/indexing_slicing_index.stderr

@@ -1,23 +1,3 @@
-error: this operation will panic at runtime
-  --> $DIR/indexing_slicing_index.rs:11:5
-   |
-LL |     x[4]; // Ok, let rustc's `const_err` lint handle `usize` indexing on arrays.
-   |     ^^^^ index out of bounds: the len is 4 but the index is 4
-   |
-   = note: `#[deny(unconditional_panic)]` on by default
-
-error: this operation will panic at runtime
-  --> $DIR/indexing_slicing_index.rs:12:5
-   |
-LL |     x[1 << 3]; // Ok, let rustc's `const_err` lint handle `usize` indexing on arrays.
-   |     ^^^^^^^^^ index out of bounds: the len is 4 but the index is 8
-
-error: this operation will panic at runtime
-  --> $DIR/indexing_slicing_index.rs:27:5
-   |
-LL |     x[N]; // Ok, let rustc's `const_err` lint handle `usize` indexing on arrays.
-   |     ^^^^ index out of bounds: the len is 4 but the index is 15
-
 error: indexing may panic.
   --> $DIR/indexing_slicing_index.rs:10:5
    |
@@ -75,5 +55,5 @@ LL |     v[M];
    |
    = help: Consider using `.get(n)` or `.get_mut(n)` instead
 
-error: aborting due to 10 previous errors
+error: aborting due to 7 previous errors