[5.5] Allow StudlyCase and snake_case migration names

[jasonmccreary]

This includes a small change to allow the developer to use a StudlyCase migration name for consistency with conventions used by other artisan commands.

This was previously with the new additions in #20760. However, since that was closed, I wanted to separate this as I believe it has value in core.

[mnabialek]

This is a bit problematic for me. Sometimes I create migrations with name like this add_whatherver_to_TABLE_table and now after this change I get add_whatherver_to_t_a_b_l_e_table. I use uppercase because tables for some clients I work are in upper case so either I have to use lowercase table name or I have manually change name of file.

[jasonmccreary]

Not sure the adoption of such a naming convention given snake_case is inherently lower. It's likely an easy fix if you are entering the migration name as snake_case, but using CAPS.

However, the opposite (going from StudlyCase to snake_case) will always be problematic unless the migration name was checked to contain a table name. Seems like a lot of code for what I would consider an edge case.

I'll see if I can add a small check to at least not "double snake_case" a migration name.