Combine builders for Vector.build and Vector.new_builder

[GregoryTravis]

Pull Request Description

We have decided to keep the old new_builder, and to combine the new and old builders into one builder.

Important Notes

Checklist

Please ensure that the following checklist has been satisfied before submitting the PR:

• The documentation has been updated, if necessary.
• Screenshots/screencasts have been attached, if there are any visual changes. For interactive or animated visual changes, a screencast is preferred.
• All code follows the
  Scala,
  Java,
  TypeScript,
  and
  Rust
  style guides. In case you are using a language not listed above, follow the Rust style guide.
• Unit tests have been written where possible.

[radeusgd]

Where is the error propagated? This is unclear to me.

Do you mean that the error will be propagated to the result of calling to_vector? Is the first such error propagated? Or last one?

[radeusgd]

Or looking at the code it seems that it is raised as a wrapped panic? That should be clarified by the docs. "Propagated" is far too vague here as it has several possible meanings.

[GregoryTravis]

Good point -- my documentation was written for build and didn't cover new_builder. I updated it to cover both cases, and added similar tests for new_builder. I changed 'propagate' to 'throw' where 'propagate' is confusing.

[radeusgd]

I think that since we are keeping new_builder, we should have at least some tests of the error propagation, for example I think we should add a new_builder variant of the

group_builder.specify "Builder should propagate an uncaught dataflow error if it is appended with .append"

test

[JaroslavTulach]

I suggest to remove Vector.new_builder.