Add some convenience helper methods on hir::Safety

[oli-obk]

Makes a lot of call sites simpler and should make any refactorings needed for #134090 (comment) simpler, as fewer sites have to be touched in case we end up storing some information in the variants of hir::Safety

[rustbot]

r? @wesleywiser

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[rustbot]

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

Some changes occurred to the CTFE machinery

cc @rust-lang/wg-const-eval

[rust-log-analyzer]

The job x86_64-gnu-llvm-18 failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

#16 exporting to docker image format
#16 sending tarball 27.7s done
#16 DONE 41.1s
##[endgroup]
Setting extra environment values for docker:  --env ENABLE_GCC_CODEGEN=1 --env GCC_EXEC_PREFIX=/usr/lib/gcc/
[CI_JOB_NAME=x86_64-gnu-llvm-18]
debug: `DISABLE_CI_RUSTC_IF_INCOMPATIBLE` configured.
---
sccache: Starting the server...
##[group]Configure the build
configure: processing command line
configure: 
configure: build.configure-args := ['--build=x86_64-unknown-linux-gnu', '--llvm-root=/usr/lib/llvm-18', '--enable-llvm-link-shared', '--set', 'rust.randomize-layout=true', '--set', 'rust.thin-lto-import-instr-limit=10', '--enable-verbose-configure', '--enable-sccache', '--disable-manage-submodules', '--enable-locked-deps', '--enable-cargo-native-static', '--set', 'rust.codegen-units-std=1', '--set', 'dist.compression-profile=balanced', '--dist-compression-formats=xz', '--set', 'rust.lld=false', '--disable-dist-src', '--release-channel=nightly', '--enable-debug-assertions', '--enable-overflow-checks', '--enable-llvm-assertions', '--set', 'rust.verify-llvm-ir', '--set', 'rust.codegen-backends=llvm,cranelift,gcc', '--set', 'llvm.static-libstdcpp', '--enable-new-symbol-mangling']
configure: target.x86_64-unknown-linux-gnu.llvm-config := /usr/lib/llvm-18/bin/llvm-config
configure: llvm.link-shared     := True
configure: rust.randomize-layout := True
configure: rust.thin-lto-import-instr-limit := 10
---
   Compiling rustc_const_eval v0.0.0 (/checkout/compiler/rustc_const_eval)
error: unused import: `self as hir`
 --> compiler/rustc_codegen_ssa/src/codegen_attrs.rs:9:17
  |
9 | use rustc_hir::{self as hir, HirId, LangItem, lang_items};
  |
  = note: `-D unused-imports` implied by `-D warnings`
  = help: to override `-D warnings` add `#[allow(unused_imports)]`

[Urgau]

r=me when green

[Urgau]

nit:

Suggested change

	pub fn is_unsafe(self) -> bool {
	#[inline]
	pub fn is_unsafe(self) -> bool {

[Urgau]

nit:

Suggested change

	pub fn is_safe(self) -> bool {
	#[inline]
	pub fn is_safe(self) -> bool {