Benchmark the PRs that have been merged since we forked

[Methuselah96]

I made #208 for introducing automated testing, however that might be too much work to get done for the next release. This issue is to track manually running benchmarks for PRs that have been merged since we forked. We're close to releasing the next RC release, and this is one of the last things to do!

PRs to benchmark:

• Hash symbols and valueOf results #17 (added benchmarks in Add benchmarks for recent changes #211; no change in performance)
• Fix #159: support isPlainObj in IE11 and constructor.name props #194 (reported below)
• throw Error when passing a instance of Record as a Record factory default values #195 (covered by Record builds from an object; no change in performance)
• Fix ordered set with map #206 (reported below)

Going forward, I would like to do the performance testing before a PR is merged, whether that is automatic or we have to do it manually.

[Methuselah96]

Regression due to #210 (see benchmark code in #211):

[Methuselah96]

Regression due to #206 (see benchmark code in #211):

[Methuselah96]

I've made separate issues for each performance regression.