Optimize Parsing & Storage of Raw Values

### Problem Description

In order to extract Perf results for builds that have multiple tests in them (https://github.com/AdoptOpenJDK/openjdk-test-tools/issues/136), we decided to store raw values in the aggregate info data structure.

The **design** is discussed: https://github.com/AdoptOpenJDK/openjdk-test-tools/issues/136#issuecomment-582062349

**Pros of current design:**

- Makes parser simpler
- Needs to done only once when the build finishes
- Different front end tools doesn't require special parsing code.
- Avoids somewhat duplication of code in the front end since front end tools would require similar logic as the one that's already there in the back end.

**Cons of current design:**

- Duplicates raw values by collecting it from different places/builds and putting them in an array

We could re-visit this design to see whether we can make this more efficient to possibly avoid duplicating raw values.

**Related PR:** https://github.com/AdoptOpenJDK/openjdk-test-tools/pull/179

Start by reading the design discussion in issue #136 and the related PR #179, which are the only implementation references provided. Determine whether the aggregate raw-value storage can be made more efficient without losing the stated support for builds with multiple tests; done means an agreed design and corresponding implementation that avoids unnecessary duplication.

Written by the indexing model from the issue text.