Support built-in diff drivers for hunk header function names

The regexes defined for each built-in driver will be used to determine
the function name for a hunk header. Each driver can specify a list of
regexes to negate and match. They can also define pattern compilation
flags if needed. These drivers only apply to text files with unified
patch type.

Following built-in drivers have been added:
- cpp
- dts
- java
- python
- rust

Support for more languages can be added as needed to match the cgit
implementation.

Change-Id: Ice5430bfed7e4aaf9f00e52e44402479984953c5