[5.8] eachById()

[halaei]

Reopen #28015

eachById() is a more efficient alternative to each(), just like chunkById() is to chunk().
I really liked to call each() but not being skip-take based makes its runtime complexity quadratic.

I also wish chunk() and each() would do id based by default. Because, in my opinion, they reserve better names but they do worse.

Changes:

• chunkById() functions in Query\Builder and Eloquent\Builder was mostly duplicate, so I removed them and move their main parts to BuildsQueries trait.
• The different parts of chunkById() in the 2 classes are now moved to defaultKeyName() function.
• The default value for $column in Query\Builder::chunkById() was 'id'. Now it is null. I guess the change is backward compatible. If it is not backward compatible this PR should be rejected.
• I changed the description of chunkById() from "Chunk the results of a query by comparing numeric IDs." to "Chunk the results of a query by comparing IDs." because it handles non-numeric ids as well.

[taylorotwell]

Probably better suited for 5.9.