Standardize file names: Fix file names in root

[ghost]

Summary

Follows up @jamischarles work on #4969.

• fix file names in root folder only
• change lint rule for file name from error to warning as suggested by @jamischarles

Details

• ran git mv to rename files
• used Atom's search and replace to replace all occurrences of a file renaming with the new filemname

Now files in root can follow standard FB practice:

- Files that primarily export types, objects or classes should use CapitalizedFileNames.js and should mirror what’s inside 1:1.
- Files that export a single function should have the function name with camelCase in it.
- Folder names should use dashes, unless they are special folders.

Test plan

Running yarn test passes. Let me know if something needs changing.

[codecov-io]

Codecov Report

Merging #5500 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #5500   +/-   ##
=======================================
  Coverage   61.67%   61.67%           
=======================================
  Files         213      213           
  Lines        7071     7071           
  Branches        3        3           
=======================================
  Hits         4361     4361           
  Misses       2709     2709           
  Partials        1        1

Impacted Files	Coverage Δ
packages/jest-config/src/valid_config.js	100% <ø> (ø)	⬆️

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[SimenB]

LGTM, pending CI. Thanks for doing this!

[cpojer]

Yeah!

[github-actions]

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