LTS 21.7 for ghc-9.4.5

[flip111]

I did a small investigation for who is interested what changes are required to the codebase to advance the GHC version used.

One minor change is needed to go to the latest GHC version of 9.2.* first #4510

This is my branch of LTS 21.7 where i gathered the findings https://github.com/flip111/purescript/tree/lts-21.7

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Findings

The following packages are not available in the LTS release and/or an older version could not be installed due to incompatible newer packages.

aeson-better-errors

Checklist: commercialhaskell/stackage#6217 (comment)
Decision: commercialhaskell/stackage#6217 (comment)

bower-json

depends on aeson-better-errors
Possibly can be removed at some point due to the new spago/registry infrastructure

cheapskate

Checklist: commercialhaskell/stackage#2670 (comment)
Decision: no active decision, implicitly removed a long time ago
Could be replaced by https://github.com/mmark-md/mmark

these

This package does no longer support the assoc compile flag. Have to investigate the implications

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Questions

1. Can bower support be removed?
2. Is it ok to change markdown parser to mmark?
3. Is aeson-better-errors used for anything other than bower.json related code (didn't look in the code yet to find out)

I couldn't compile yet so compile errors from newer packages is still an open question as well.