Enable pending formatter features

[Blacksmoke16]

Enables the first batch of ready formatter features as called out in #13002.

• Formatter: add & to yielding methods without a block parameter #12951 (-Dmethod_signature_yield)
• Trailing commas for multiline def / macro / fun parameter lists #13169 (-Ddef_trailing_comma)
• Formatter: Add more whitespace around ProcLiterals #14209 (-Dproc_literal_whitespace)

NOTE: Depends on #14713

[straight-shoota]

I noticed an issue: #14209 and #14075 (partially) are backwards-incompatible changes. Two formatters, one with the changes enabled and one with it disabled, cannot agree on a common accepted style as a valid variant.
This can cause friction related to crystal upgrades, which should be avoidable.

We could ensure a smooth transition by first releasing a version of the formatter which doesn't change old style to new style, but accepts the new style and does not change it back to old style.

For example the change in #12951 is backwards compatible. The current formatter accepts the & style, but doesn't enforce it.

[Blacksmoke16]

Alright, I'll see if I can put something together for that to include in this release. Then can release the part that'll migrate old to new in the next one.

[Blacksmoke16]

CI seems to be failing due to:

docker: Error response from daemon: unauthorized: authentication required.

🤔

[straight-shoota]

Looks like Docker hub was unavailable... There are some legitimate spec failures though (e.g. https://github.com/crystal-lang/crystal/actions/runs/11023991475/job/30616353981?pr=14718).

[Blacksmoke16]

I figured there would be, discovered #15033 when running the specs locally so figured I'd let CI run while figuring what was going on there.

[crysbot]

This pull request has been mentioned on Crystal Forum. There might be relevant details there:

https://forum.crystal-lang.org/t/upcoming-release-1-15-0/7537/1