Removal of sub-component targets breaks HLS/hie-bios: we need regression test

**UPDATE**: the change was reverted but let's leave the ticket open until we have a regression test.

**Describe the bug**

https://github.com/haskell/cabal/pull/8966 removes cabal-install's support for sub-module targets.

But this (mis-)feature is used by HLS via hie-bios to determine the flags for a component.

In particular it makes a call to `cabal v2-repl `

**To Reproduce**
Steps to reproduce the behavior:

Have a prerelease of cabal-install on your PATH
```
$ cabal repl
Warning: this is a debug build of cabal-install with assertions enabled.
Error: [Cabal-7121]
Failed extracting script block: `{- cabal:` start marker not found
```
or
```
$ haskell-language-server
...
Loading the module 'so-and-so.hs' failed.

It may not be listed in your .cabal file!
Perhaps you need to add `so-and-so` to other-modules or exposed-modules.
```

**Expected behavior**
HLS should at least work.
Perhaps some work needs to be done to migrate HLS/hie-bios off this feature.
Alternatively the MR could be reverted.

**System information**
tested using cabal-head

Start by reproducing the `cabal v2-repl` call with a path to a `.hs` file, then inspect the cabal-install handling of sub-module targets and the HLS/hie-bios integration described here. Add a regression test covering a component target or source-file path and verify that HLS can determine the component flags without the reported failure.

Written by the indexing model from the issue text.