Tracking issue for const `Pin` methods

[CDirkx]

Constify methods of core::pin::Pin under the feature const_pin.

Implementation: #76655

Methods in const_pin (stable since #130136):

• new
• new_unchecked
• get_ref
• into_ref
• get_mut
• get_unchecked_mut
• static_ref
• static_mut

Methods in const_pin2:

• into_inner
• into_inner_unchecked

The const_pin2 methods will need #[rustc_allow_const_fn_unstable(const_precise_live_drops)] but that has been approved here.

[ecstatic-morse]

As you mention in #76655 PR, the implementation of some of these methods depends on the unstable const_precise_live_drops feature. Future readers should check the status of that feature before attempting to stabilize these. #76618 will ensure that this does not happen by accident.