[Sync EN] fix(mb-strlen): document invalid encoding ValueError and add shared snippets (#5418)

[github-actions]

Commit: https://github.com/php/doc-en/commit/8465ca6ec4bbcf79583ecd057860164dd9c7e385
PR: https://github.com/php/doc-en/pull/5418

Archivos ES a actualizar

• language-snippets.ent
• reference/mbstring/functions/mb-encoding-aliases.xml
• reference/mbstring/functions/mb-internal-encoding.xml
• reference/mbstring/functions/mb-strlen.xml