Use GitHub teams as code owners (#6114)

The teams named in this revised version of the `CODEOWNERS` file are
currently configured with the same members as are listed in the file
now.

We wanted a single member of the selected team to be assigned as a
reviewer, but listing people explicitly in CODEOWNERS causes all the
named people to be assigned. Using teams instead allows us to configure
the load-balancing policy.

This also will allow us to add and remove reviewers without needing a PR
every time.

CODEOWNERS

@@ -19,24 +19,24 @@
 # work on this project. We gratefully welcome reviews from other contributors,
 # but we don't believe it's fair to ask volunteers to respond quickly.
 
-# TODO: use GitHub teams instead of individual usernames
-
-# If none of the later patterns match, assign to anyone:
-* @alexcrichton @cfallin @elliottt @fitzgen @jameysharp @pchickey
+# If none of the later patterns match, assign to anyone. This team is the
+# parent of all the other teams and automatically includes everyone on those
+# teams.
+* @bytecodealliance/wasmtime-default-reviewers
 
 # Some parts of the project require more specialized knowledge. In those areas
 # we designate smaller groups who are more likely to be aware of who's working
 # in specific areas.
 
 # Wasmtime
-/crates/   @alexcrichton @fitzgen @jameysharp @pchickey
-/examples/ @alexcrichton @fitzgen @jameysharp @pchickey
-/src/      @alexcrichton @fitzgen @jameysharp @pchickey
-/tests/    @alexcrichton @fitzgen @jameysharp @pchickey
+/crates/   @bytecodealliance/wasmtime-core-reviewers
+/examples/ @bytecodealliance/wasmtime-core-reviewers
+/src/      @bytecodealliance/wasmtime-core-reviewers
+/tests/    @bytecodealliance/wasmtime-core-reviewers
 
 # Cranelift/Winch compilers
-/cranelift/ @cfallin @elliottt @fitzgen @jameysharp
-/winch/     @cfallin @elliottt @fitzgen @jameysharp
+/cranelift/ @bytecodealliance/wasmtime-compiler-reviewers
+/winch/     @bytecodealliance/wasmtime-compiler-reviewers
 
 # Fuzz testing
-/fuzz/ @alexcrichton @elliottt @fitzgen @jameysharp
+/fuzz/ @bytecodealliance/wasmtime-fuzz-reviewers