[analyzer] [NFC] [tests] Move plist-based diagnostics tests to separate files,...

[analyzer] [NFC] [tests] Move plist-based diagnostics tests to separate files, use diff instead of a FileCheck

Some of the analyzer tests check the exact plist output, in order to
verify that the diagnostics produced is correct.
Current testing setup has many issues:

plist output clobbers tests, making them harder to read
it is impossible to debug test failures given error messages from FileCheck.
The only recourse is manually creating the files and using the diff
again, it is impossible to update the tests given the error message:
the only process is a tedious manual one,
going from a separate plist file to CHECK directives.

This patch offers a much better approach of using "diff" directly in place of FileCheck,
and moving tests to separate files.

Generated using the following script:

```
import os
import glob
import re
import subprocess

diagnostics_key = "// CHECK:  <key>diagnostics</key>"

def process_file(f, data):
    idx = data.index(diagnostics_key)
    plist_out_f = 'ExpectedOutputs/plists/%s.plist' % f
    plist_out_folder = os.path.join('ExpectedOutputs/plists/', os.path.dirname(f))
    plist_data = data[idx:]
    plist_data = plist_data.replace('// CHECK: ', '')
    plist_data = plist_data.replace('// CHECK-NEXT: ', '')
    plist_data += "</dict>\n</plist>\n"
    data = data[:idx]

    ptn = re.compile("FileCheck --?input-file(=| )(%t|%t\.plist) %s")

    if not ptn.findall(data):
        print "none found =/ skipping..."
        return

    data = ptn.sub(lambda m: "tail -n +11 %s | diff -u -w - %%S/../%s" % (m.group(2), plist_out_f), data)

    with open(f, 'w') as out_f:
        out_f.write(data)

    subprocess.check_call(["mkdir", "-p", plist_out_folder])
    with open(plist_out_f, 'w') as out_f:
        out_f.write(plist_data)

def main():
    files = glob.glob("**/*.*")
    for f in files:
        with open(f) as f_handler:
            data = f_handler.read()
        if diagnostics_key in data:
            print "Converting %s" %f
            process_file(f, data)

if __name__ == "__main__":
    main()
```

Differential Revision: https://reviews.llvm.org/D50545

llvm-svn: 339475