Move validation from FindDeapexerProviderForModule to rdeps

FindDeapexerProviderForModule raises an exception if multiple apexes in
the tree has an export dep on the java module. In prepartation to
support multiple prebuilts, move this error check out of
FindDeapexerProviderForModule and into rdeps. i.e. raise an exception
only if an rdep calls DexJarBuildPath

- This should be a no-op for now.
- In the short-term future, a java import module will be allowed to have
  multiple deapexers. An error will be raised if anyone actually tries
  to depend on the dexjar
- In the long-term future, this function will be removed. All processing
  will be done at the prebuilt apex level and not at the prebuilt java
  library level

Since this check now happens in the moduleCtx of rdeps, add some
additional props to unit tests to ensure that it does not exit early on
unrelated validation checks (e.g. hidden_api prop is not set)

Test: go test ./apex ./java
Bug: 308790457

Change-Id: I3323d993c1ea8f43305834cae8e65b6fe41dfefd