- get rid of SourceLocation.source for memory efficiency
- move source location generation logic transform phase into the parser
  itself so that SourceLocation.source is no longer needed
  - move v-for expression parsing into the parser itself
  - added nameLoc on AttributeNode for use in transformElement

Tests are not passing yet.

magic-string's trim method uses a regex check for aborting which turns
out to be extremely expensive - it cna take up to 10% time in total SFC
compilation! The usage here is purely aesthetic so simply removing it
for a big perf gain is well worth it.

Previously, many CodegenContext.push() calls were unnecessarily
iterating through the entire pushed string to find newlines, when we
already know the newline positions for most of calls. Providing fast
paths for these calls significantly improves codegen performance when
source map is needed.

In benchmarks, this PR improves full SFC compilation performance by ~6%.