Replace panic with ModuleErrorf

This is a followup cleanup for aosp/2876754 and replaces panic with
ctx.ModuleErrorf. The latter creates a more expressive build error.

Implementation details
- export moduleErrorf interface from build/soong/android. This minimal
  interface will be used as a parameter for `DexJarBuildPath`
- Add ModuleErrorf to the function signature of DexJarBuildPath. This
  parameter only gets used for Import and SdkLibraryImport structs.
  These two can have duplicate deapexer definitions, and ModuleErrorf
  will be used to report that error
- Create a minimal implementation of `ModuleErrorf` in tests of java and
  apex

Test: m nothing --no-skip-soong-tests
Change-Id: I0febec651f40c3f04deb957e64133c94b80fbd78