Improve detection of REST requests

[bobbingwide]

In Gutenberg 8.4.0 there are a number of requests which are not being traced as REST requests since the URL form is not recognised. The Block directory search is one of them.

Here's the trace output showing that wp-json/wp/v2/blocks is detected but not /wp-json/__experimental/block-directory/search, which is used twice the first time a search is performed.

/wp-json/wp/v2/blocks?per_page=100&_locale=user,,1.488032,7.3.8,1291,4780,743,31,1016,50,30,14,55,0.15688490867615,C:/apache/htdocs/wp-a2z/bwtrace/bwtrace.rest.4,189,0,21364,127.0.0.1,1.485162,2020-07-06T07:46:42+00:00,Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML; like Gecko) Chrome/83.0.4103.116 Safari/537.36,GET
/wp-json/__experimental/block-directory/search?_locale=user,,0.917202,7.3.8,1291,4648,675,31,936,50,30,14,26,,,,,11713,127.0.0.1,0.913878,2020-07-06T07:47:03+00:00,Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML; like Gecko) Chrome/83.0.4103.116 Safari/537.36,OPTIONS
/wp-json/__experimental/block-directory/search?term=bea&_locale=user,,1.540149,7.3.8,1291,4657,684,31,947,50,30,14,26,,,,,11805,127.0.0.1,1.534153,2020-07-06T07:47:04+00:00,Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML; like Gecko) Chrome/83.0.4103.116 Safari/537.36,GET