Reland "Change the mac builder default to be either 10.13 or 10.15."

This is a reland of 11c26e5e

Original change's description:
> Change the mac builder default to be either 10.13 or 10.15.
> 
> Once the hosts are all upgraded to 10.15 we will remove the 10.13 option.
> 
> Bug: 1121185
> Change-Id: I3177749f79ddd16b9d725693f21e79ebd752c22c
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2412757
> Commit-Queue: Erik Staab <estaab@chromium.org>
> Auto-Submit: Erik Staab <estaab@chromium.org>
> Reviewed-by: Garrett Beaty <gbeaty@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#807218}

Bug: 1121185
Change-Id: I0b4e69122fc7b80165ca2abbd2542c24ba88d0d5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2413529
Auto-Submit: Erik Staab <estaab@chromium.org>
Reviewed-by: Garrett Beaty <gbeaty@chromium.org>
Commit-Queue: Garrett Beaty <gbeaty@chromium.org>
Cr-Commit-Position: refs/heads/master@{#807488}

infra/config/generated/cr-buildbucket-dev.cfg

@@ -136,7 +136,7 @@ buckets {
       swarming_host: "chromium-swarm-dev.appspot.com"
       swarming_tags: "vpython:native-python-wrapper"
       dimensions: "cpu:x86-64"
-      dimensions: "os:Mac-10.13"
+      dimensions: "os:Mac-10.13|Mac-10.15"
       recipe {
         name: "swarming/staging"
         cipd_package: "infra/recipe_bundles/chromium.googlesource.com/chromium/tools/build"

infra/config/lib/builders.star

@@ -65,7 +65,8 @@ os = struct(
     MAC_10_14 = os_enum("Mac-10.14", os_category.MAC),
     MAC_10_15 = os_enum("Mac-10.15", os_category.MAC),
     MAC_11_0 = os_enum("Mac-11.0", os_category.MAC),
-    MAC_DEFAULT = os_enum("Mac-10.13", os_category.MAC),
+    # TODO(crbug/1121185): Remove 10.13 once builders have been migrated to 10.15.
+    MAC_DEFAULT = os_enum("Mac-10.13|Mac-10.15", os_category.MAC),
     MAC_ANY = os_enum("Mac", os_category.MAC),
     WINDOWS_7 = os_enum("Windows-7", os_category.WINDOWS),
     WINDOWS_8_1 = os_enum("Windows-8.1", os_category.WINDOWS),

infra/config/subprojects/chromium/try.star

@@ -1115,7 +1115,7 @@ try_.chromium_mac_builder(
     branch_selector = branches.STANDARD_RELEASES,
     goma_jobs = goma.jobs.J150,
     main_list_view = settings.main_list_view_name,
-    os = os.MAC_10_13,
+    os = os.MAC_DEFAULT,
     tryjob = try_.job(),
 )
 
@@ -1167,7 +1167,7 @@ try_.chromium_mac_builder(
     name = "mac_chromium_compile_dbg_ng",
     branch_selector = branches.STANDARD_RELEASES,
     goma_jobs = goma.jobs.J150,
-    os = os.MAC_10_13,
+    os = os.MAC_DEFAULT,
     main_list_view = settings.main_list_view_name,
     tryjob = try_.job(cancel_stale = False),
 )

infra/config/subprojects/chromium/versioned/m85/buckets/try.star

@@ -445,14 +445,14 @@ try_.chromium_linux_builder(
 try_.chromium_mac_builder(
     name = "mac-rel",
     goma_jobs = goma.jobs.J150,
-    os = os.MAC_10_13,
+    os = os.MAC_DEFAULT,
     tryjob = try_.job(),
 )
 
 try_.chromium_mac_builder(
     name = "mac_chromium_compile_dbg_ng",
     goma_jobs = goma.jobs.J150,
-    os = os.MAC_10_13,
+    os = os.MAC_DEFAULT,
     tryjob = try_.job(),
 )