Add support for Jar to Jar transformation to JarInfer

[navahgar]

This adds support for annotating jar files, as opposed to creating an astubx file on the side.

Summary of changes:

• Added support to annotate jar files with the annotations inferred by the analysis in JarInfer.
• Added a flag in JarInfer CLI to enable annotating jar files.
• Tested annotated jar files by checking for expected annotations.
• Added the expected annotations in the sources used for tests.

[lazaroclapp]

Lots of comments because this is lots of code, but overall the approach and code looks good to me.

A few general points:

• Not sure I understand the logic for the source based test cases (the one using a test project I get, just the one involving getToyTestSrcWithExpectAnnotations doesn't quite make sense to me.
• Please change the PR title and description to something that would make for a useful documenting commit message once we squash and merge. Otherwise we'll be scratching our heads a year from now trying to figure out what JarInfer (#316) was ;)
• Probably worth adding a few javadocs at the class and public method level
• Also, I just realized this is missing in some other files, but the license information should be at the top of each source files, as in https://github.com/uber/NullAway/blob/master/nullaway/src/main/java/com/uber/nullaway/NullAway.java (will send you the internal guidelines in a moment)

[navahgar]

Thanks for the detailed comments. Addressed them. PTAL.

[kageiit]

Can you please add a more descriptive title and a quick summary of the top changes maybe to now we changed jarinfer

[navahgar]

Summary of changes:

• Added support to annotate jar files with the annotations inferred by the analysis in JarInfer.
• Added a flag in JarInfer CLI to enable annotating jar files.
• Tested annotated jar files by checking for expected annotations.
• Added the expected annotations in the sources used for tests.

[navahgar]

Can you please add a more descriptive title and a quick summary of the top changes maybe to now we changed jarinfer

Updated the title and added a summary.

[lazaroclapp]

LGTM, see comment about missing Javadoc, and also please make sure the title of the commit is under 80 characters (we don't always follow this, but we probably should :), you can still have a longer explanation inside the message body).

Suggestion:

Add support for Jar to Jar transformation to JarInfer

This adds support for annotating jar files, as opposed to creating an 
astubx file on the side. 

Summary of changes:
...

Followed for the stuff you already have. Once those two are addressed, feel free to land it.

[msridhar]

Just a code style comment that probably should be fixed in a follow-up rather than here.