Optimize source generation
Since StringBuilder is fluent, we can optimize some of the source
generation utilities to have less bytecode. Also mark FIXMEs for
future improvement, as these would allow better devirtualization.
Furthermore we expose Class-based cast/assign operations, which
trim down code duplication a tiny bit.
Change-Id: I32d9d9321992effe0bec1423990208a92c1f780b
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>
(cherry picked from commit
3a1da8e23805b36351172eeb7f11bc134821ee36)