policy: Add policy CMP0052

This policy switches between the old EVIS parser and the new, faster
parser.
tests: Add tests for syntax corner cases and CMP0052
EVIS: Reimplement using custom parsing code

Testing the configure (no generate) step with ParaView shows ~20%
performance improvement.

In terms of complete configure/generate steps, further testing with
ParaView shows a 20% performance improvement over 2.8.12.2 with Unix
Makefiles and minimal with Ninja. Ninja is less because it generate step
is the expensive part (future work will address this) by a long shot and
these changes help the configure step for the most part.
Merge topic 'dev/faster-evis' into next

f671858a EVIS: Reimplement using custom parsing code
ddcf0583 tests: Add tests for syntax corner cases and CMP0052
340345f7 policy: Add policy CMP0052