chore: [TL migration] rename getByPlaceholder to getByPlaceholderText (or provide an alias)

[mdjastrzebski]

Describe the Feature

Currently we have getByPlaceholder (and related queries). However, both RTL and deprecated TL/RN use getByPlaceholderText.

This seems to be consistent with other RTL, TL/RN names likes getByLabelText, getByHintText, etc.

Possible Implementations

1. Rename getByPlaceholder -> getByPlaceholderText
2. Add alias for getByPlaceholderText

Selected option should be mentioned in the migration guide.

My preferred option would be 1 (rename), as it would keep things simple & consitent.

Related Issues

This is part of migration to official TL repo.

CC: @thymikee @Esemesek @cross19xx

[thymikee]

I'm in for option 1, the change is easy enough to migrate without too much effort.

[thymikee]

Closed via #455