RFR: 7903600: Add more tests for unsupported types [v2]

[Jorn Vernee]

> Add more tests for unsupported types. See the new TestUnsupportedTypes.java
> 
> While working on this, I also noticed several cases of dead code: `FunctionalInterfaceScanner` is completely unused, and `InMemoryJavaCompiler::jfoFromByteArray` and `InMemoryJavaCompiler::jfoFromString` (and its caller in `OutputFactory`) are unused as well. I've removed them in this PR.
> 
> Changes in this PR:
> - I'm passing in the error stream PrintWriter that we create in the test all the way down to UnsupportedFilter, so that it can write to it instead of `System.err`. Then we can check what was written in the test. 
> - I've added warning print outs for the different reasons why we are skipping declarations. Some of these were missing.
> - I've removed a check for ValueLayouts that are larger than 8 bytes in `visitVariable`. If the type of a variable is an unsupported primitive, we already filter it out earlier on in the method, so there's no need to check again.
> - I've added a missing `Skip.with` in `visitVariable`, so that we will filter out (global) variables with unsupported function types.
> - I've added skipping of typedefs when they have an unsupported type or a type that does not have a layout. For the latter, I've also had to remove a test case that checked if we generated a typedef class for an undefined struct type. Since the struct is undefined, I believe we should not generate a typedef binding class for that case.
> 
> The new test covers all the unsupported type cases that are handled by TestUnsupportedTypes.

Jorn Vernee has updated the pull request incrementally with one additional commit since the last revision:

  review comments

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Changes:
  - all: https://git.openjdk.org/jextract/pull/152/files
  - new: https://git.openjdk.org/jextract/pull/152/files/cb930413..92efaafa

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jextract&pr=152&range=01
 - incr: https://webrevs.openjdk.org/?repo=jextract&pr=152&range=00-01

  Stats: 18 lines in 2 files changed: 0 ins; 4 del; 14 mod
  Patch: https://git.openjdk.org/jextract/pull/152.diff
  Fetch: git fetch https://git.openjdk.org/jextract.git pull/152/head:pull/152

PR: https://git.openjdk.org/jextract/pull/152