url: avoid instanceof for WHATWG URL

[mscdex]

This PR replaces instanceof checks with symbol checks. Various relevant results:

                                                                             improvement confidence      p.value
 url/url-searchparams-read.js n=50000000 param="nonexistent" method="get"       195.08 %        *** 5.548226e-41
 url/url-searchparams-read.js n=50000000 param="nonexistent" method="getAll"    174.48 %        *** 3.225875e-29
 url/url-searchparams-read.js n=50000000 param="nonexistent" method="has"       190.68 %        *** 9.000669e-32
 url/url-searchparams-read.js n=50000000 param="one" method="get"               269.63 %        *** 2.180791e-33
 url/url-searchparams-read.js n=50000000 param="one" method="getAll"            111.73 %        *** 1.724534e-25
 url/url-searchparams-read.js n=50000000 param="one" method="has"               266.25 %        *** 5.498456e-33
 url/url-searchparams-read.js n=50000000 param="three" method="get"             203.56 %        *** 2.754902e-45
 url/url-searchparams-read.js n=50000000 param="three" method="getAll"          108.95 %        *** 1.790912e-35
 url/url-searchparams-read.js n=50000000 param="three" method="has"             198.65 %        *** 1.896093e-32
 url/url-searchparams-read.js n=50000000 param="two" method="get"               248.88 %        *** 4.737990e-41
 url/url-searchparams-read.js n=50000000 param="two" method="getAll"            112.93 %        *** 2.182157e-31
 url/url-searchparams-read.js n=50000000 param="two" method="has"               224.41 %        *** 2.056153e-30
 url/whatwg-url-properties.js n=10000000 prop="origin" input="auth"              12.59 %         ** 0.0035532598
 url/whatwg-url-properties.js n=10000000 prop="origin" input="dot"               10.53 %         ** 0.0041671062
 url/whatwg-url-properties.js n=10000000 prop="origin" input="file"              72.86 %        *** 0.0004049447
 url/whatwg-url-properties.js n=10000000 prop="origin" input="idn"                5.76 %            0.1494657794
 url/whatwg-url-properties.js n=10000000 prop="origin" input="javascript"        54.73 %         ** 0.0018129659
 url/whatwg-url-properties.js n=10000000 prop="origin" input="long"              10.20 %          * 0.0429791847
 url/whatwg-url-properties.js n=10000000 prop="origin" input="percent"            1.84 %            0.3920201593
 url/whatwg-url-properties.js n=10000000 prop="origin" input="short"             11.54 %        *** 0.0001064664
 url/whatwg-url-properties.js n=10000000 prop="origin" input="ws"                10.64 %         ** 0.0074980105

CI: https://ci.nodejs.org/job/node-test-pull-request/6707/

/cc @nodejs/url

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines

Affected core subsystem(s)

• url-whatwg