Add default support for arrays of all sizes

[saeubank]

Currently only arrays of up to size 32 support Default.
This expands Default to be allowed for arrays of all sizes.

rust-lang/libs-team#153

[rustbot]

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[rustbot]

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If this PR contains changes to any rust-lang/rust public library APIs then please comment with @rustbot label +T-libs-api -T-libs to tag it appropriately. If this PR contains changes to any unstable APIs please edit the PR description to add a link to the relevant API Change Proposal or create one if you haven't already. If you're unsure where your change falls no worries, just leave it as is and the reviewer will take a look and make a decision to forward on if necessary.

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[rust-log-analyzer]

The job mingw-check failed! Check out the build log: (web) (plain)

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

configure: rust.debug-assertions := True
configure: rust.overflow-checks := True
configure: llvm.assertions      := True
configure: dist.missing-tools   := True
configure: build.configure-args := ['--enable-sccache', '--disable-manage-submodu ...
configure: writing `config.toml` in current directory
configure: 
configure: run `python /checkout/x.py --help`
Attempting with retry: make prepare
---
    Checking rand v0.7.3
    Checking alloc v0.0.0 (/checkout/library/alloc)
    Checking std v0.0.0 (/checkout/library/std)
    Checking core v0.0.0 (/checkout/library/core)
error[E0599]: the function or associated item `default` exists for array `[DoesNotImplDefault; 0]`, but its trait bounds were not satisfied
    |
    |
303 |     struct DoesNotImplDefault;
    |     ------------------------- doesn't satisfy `DoesNotImplDefault: Default`
304 |
305 |     let _arr = <[DoesNotImplDefault; 0]>::default();
    |                                           ^^^^^^^ function or associated item cannot be called on `[DoesNotImplDefault; 0]` due to unsatisfied trait bounds
    = note: the following trait bounds were not satisfied:
    = note: the following trait bounds were not satisfied:
            `DoesNotImplDefault: Default`
            which is required by `[DoesNotImplDefault; 0]: Default`
help: consider annotating `DoesNotImplDefault` with `#[derive(Default)]`
303 |     #[derive(Default)]
    |

For more information about this error, try `rustc --explain E0599`.

[saeubank]

@rustbot label +T-libs-api -T-libs

[saeubank]

@bors try

[bors]

@saeubank: 🔑 Insufficient privileges: not in try users

[dtolnay]

I am very skeptical that the library API team would be on board with breaking the [T; 0] impl. I'll go ahead and close this PR.

However, the team is interested in approaches that would allow arbitrarily large [T; N] to implement Default, as long as the 0 case continues to work as it currently does. This is already tracked in #61415.