* To avoid calling rb_gc_writebarrier() with an immediate value in gen_write_barrier(),
  and avoid the LIR jump issue.

These macros have been defined here and there, so collect them.

* ZJIT: Add dump to file for --zjit-stats

* ZJIT: Rename --zjit-stats=quiet to --zjit-stats-quiet

Its definition changes depending on e.g. whether there is YJIT in the
build.

This implements Shopify#854:

- Splits boot-time and enable-time initialization,
  tracks progress with `InitializationState` enum

- Introduces `RubyVM::ZJIT.enable` Ruby method for
  enabling the JIT lazily, if not already enabled

- Introduces `--zjit-disable` flag, which can be
  used alongside the other `--zjit-*` flags but
  prevents enabling the JIT at boot time

- Adds ZJIT infra to support JIT hooks, but this
  is not currently exercised (Shopify/ruby#667)

Left for future enhancements:

- Support kwargs for overriding the CLI flags in
  `RubyVM::ZJIT.enable`

Closes Shopify#854

Storing the tagged block handler in profiles is not GC-safe (nice catch,
Kokubun). Store the untagged block handler instead.

Fix bug in https://github.com/ruby/ruby/pull/15051

I made a special kind of `ProfiledType` that looks at specific objects, not just their classes/shapes (https://github.com/ruby/ruby/pull/15051). Then I profiled some of our benchmarks.

For lobsters:

```
Top-6 invokeblock handler (100.0% of total 1,064,155):
        megamorphic: 494,931 (46.5%)
   monomorphic_iseq: 337,171 (31.7%)
        polymorphic: 113,381 (10.7%)
  monomorphic_ifunc:  52,260 ( 4.9%)
  monomorphic_other:  38,970 ( 3.7%)
        no_profiles:  27,442 ( 2.6%)
```

For railsbench:

```
Top-6 invokeblock handler (100.0% of total 2,529,104):
   monomorphic_iseq: 834,452 (33.0%)
        megamorphic: 818,347 (32.4%)
        polymorphic: 632,273 (25.0%)
  monomorphic_ifunc: 224,243 ( 8.9%)
  monomorphic_other:  19,595 ( 0.8%)
        no_profiles:     194 ( 0.0%)
```

For shipit:

```
Top-6 invokeblock handler (100.0% of total 2,104,148):
        megamorphic: 1,269,889 (60.4%)
        polymorphic:   411,475 (19.6%)
        no_profiles:   173,367 ( 8.2%)
  monomorphic_other:   118,619 ( 5.6%)
   monomorphic_iseq:    84,891 ( 4.0%)
  monomorphic_ifunc:    45,907 ( 2.2%)
```

Seems like a monomorphic case for a specific ISEQ actually isn't a bad way of going about this, at least to start...