Inform LLVM that &str has length <= isize::MAX

[Darksonn]

When &str appears as a function argument, we can inform LLVM that the length has a restricted range similar to what's already done for slices.

The tests/codegen-llvm/function-arguments.rs file has a test that looks like it intended to check this scenario, but the fn str function uses a &[u8] argument rather than &str. Since there's also another identical fn slice with an &[u8] argument in this test, this appears to be an oversight.

rust/tests/codegen-llvm/function-arguments.rs

Lines 183 to 187 in 36b04f3

	// CHECK: @slice(
	// CHECK-SAME: ptr noalias nofree noundef nonnull readonly{{( captures\(address, read_provenance\))?}} %_1.0,
	// CHECK-SAME: [[USIZE]] noundef range({{i32 0, -2147483648|i64 0, -9223372036854775808}}) %_1.1)
	#[no_mangle]
	pub fn slice(_: &[u8]) {}

rust/tests/codegen-llvm/function-arguments.rs

Lines 206 to 210 in 36b04f3

	// CHECK: @str(
	// CHECK-SAME: ptr noalias nofree noundef nonnull readonly{{( captures\(address, read_provenance\))?}} %_1.0,
	// CHECK-SAME: [[USIZE]] noundef range({{i32 0, -2147483648|i64 0, -9223372036854775808}}) %_1.1)
	#[no_mangle]
	pub fn str(_: &[u8]) {}

This issue was discovered by an LLM, but the PR was implemented by hand.