This puts the behavior introduced in 573b8611bc behind the new flag
`alwaysCompileGeneratedCode` to not break users that might have relied
on this behavior.
Inlcuded fixes:
- include preamble in generated source map
- always add a mapping for line/col 0 so that the
generated sourcemap is not sparse
- use a uniue sourceUrl for inline templates even
in the AOT case