conrad_v8_merged to master merge

[IgnoredAmbience]

Ticket to track features merged/cherry-picked from Conrad's v8 branch back into master.

New features in branch (tick when done):

• [x] Esprima parser
• [x] String constructor (needs proof)
• [x] String function (needs proof)

Then all that remains is V8 specific parts.

I've noted a few testcases that have regressed between two of my analysis testruns, they require further research into whether they're genuine regressions or artefacts of a dirty merge:

• tests/test262/ch15/15.2/15.2.3/15.2.3.9/15.2.3.9-2-d-1.js
• tests/test262/ch15/15.2/15.2.3/15.2.3.8/15.2.3.8-2-c-1.js
• tests/test262/ch15/15.2/15.2.3/15.2.3.8/15.2.3.8-2-a-7.js
• tests/test262/ch15/15.2/15.2.3/15.2.3.9/15.2.3.9-2-a-9.js

[IgnoredAmbience]

The string constructor and call function implementations have been extracted onto their own branch for proving.