Better errors for manyIndex

[jamesdbrock]

Return the parse error message of the phrase parser which failed instead of “Expected more phrases.” Also how many phrases were expected.

https://github.com/purescript-contrib/purescript-parsing/issues/210

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Checklist:

• [x] Added the change to the changelog's "Unreleased" section with a link to this PR and your username
• [x] Linked any existing issues or proposals that this pull request should close
• [x] Updated or added relevant documentation in the README and/or documentation directory
• [x] Added a test for the contribution (if applicable)