servo: Merge #16972 - style: Move all the style sharing code outside matching.rs (from emilio:sanity-is-important-most-of-the-time); r=bholley

This is just a code health change. I want to move it away to keep matching.rs as
simple as possible.

Source-Repo: https://github.com/servo/servo
Source-Revision: 03fbea4ec8af3ef6c5c621974b3c52cd755ed287

UltraBlame original commit: fa744ead203d68703ee82790db81440d5584615e

Author: marco-c

servo/components/style/context.rs

@@ -172,12 +172,6 @@ gecko_bindings
 :
 structs
 ;
-use
-matching
-:
-:
-StyleSharingCandidateCache
-;
 #
 [
 cfg
@@ -250,6 +244,12 @@ shared_lock
 :
 StylesheetGuards
 ;
+use
+sharing
+:
+:
+StyleSharingCandidateCache
+;
 #
 [
 cfg

servo/components/style/lib.rs

@@ -1024,6 +1024,10 @@ shared_lock
 ;
 pub
 mod
+sharing
+;
+pub
+mod
 stylist
 ;
 #