Update plural rules.

Update rules for French, Italian, Spanish and Portuguese based on CLDR v47
https://php-gettext.github.io/Languages/#47

Closes #18740

Fix default locale path.

Small cleanups and typo fixes.

Drop psalm

Update composer branch aliases for split packages. (#18259)

Update dependency constraints for the split packages.

This should allow using/testing the 5.next branch of the split packages.

Update dependency constraints for the split packages.

This should allow using/testing the 5.next branch of the split packages.

Merge branch '4.x' into 4.next-merge

# Conflicts:
#	VERSION.txt

Merge branch '4.x' into 4.next-merge

# Conflicts:
#	VERSION.txt

Merge branch '4.x' into 4.next-merge

# Conflicts:
#	VERSION.txt