(v7.x backport) url: updates to the WHATWG URL parser

[TimothyGu]

This pull request brings the WHATWG URL implementation in v7.x up to speed with master, including the code itself, the docs, and the tests.

Note: #12042 is not backported since #11956 (which it depends on) has not been backported yet.

Backports of (in the order they were landed to master):

• url: extend URLSearchParams constructor #11060 url: extend URLSearchParams constructor
• url: enforce valid UTF-8 in WHATWG parser #11436 url: enforce valid UTF-8 in WHATWG parser
• url: call toString before valueOf when stringifying #11737 url: call toString before valueOf when stringifying
• url: spec-compliant URLSearchParams serializer #11626 url: spec-compliant URLSearchParams serializer
• src: remove explicit UTF-8 validity check in url #11859 src: remove explicit UTF-8 validity check in url
• url: spec-compliant URLSearchParams parser #11858 url: spec-compliant URLSearchParams parser
• lib: use Object.create(null) directly #11930 lib: use Object.create(null) directly (only the part that adds an explicit class for url[context])
• url: add ToObject method to native URL class #12056 url: add ToObject method to native URL class
• src, url: WHATWG URL C++ parser cleanup #11917 src, url: WHATWG URL C++ parser cleanup
• url: change path parsing for non-special URLs #12058 url: change path parsing for non-special URLs
• url: stricter domainTo*() argument checking #12134 url: stricter domainTo*() argument checking
• url: avoid instanceof for WHATWG URL #11690 url: avoid instanceof for WHATWG URL
• url: trim leading slashes of file URL paths #12203 url: trim leading slashes of file URL paths
• url: remove javascript URL special case #12331 url: remove javascript URL special case
• url: disallow invalid IPv4 in IPv6 parser #12315 url: disallow invalid IPv4 in IPv6 parser
• url: clean up WHATWG URL origin generation #12252 url: clean up WHATWG URL origin generation
• url: improve WHATWG URL inspection #12253 url: improve WHATWG URL inspection
• src: clean up WHATWG URL parser, round 2 #12251 src: clean up WHATWG URL parser, round 2

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

url

[TimothyGu]

CI: https://ci.nodejs.org/job/node-test-pull-request/7508/

[jasnell]

rubber stamp LGTM