Use LTS and LTS-1 Node versions (#28048)

Summary:
Previous config used Node10 and NodeLTS executors, but the naming wasn't accurate. As of today, Node 12 is LTS, Node 10 is also LTS but entering maintenance in April: https://nodejs.org/en/about/releases/

This PR switches all jobs to use Node 12 as nodelts, and renames test_js_lts to test_js_prevlts to reflect it's use of Node 10 (the previous Node LTS release). The executors are named NodeLTS and NodeLTSPrev. Later this year, we can switch these to use Node 14 and Node 12 as Node 10 goes into maintenance.

## Changelog

[Internal]
Pull Request resolved: https://github.com/facebook/react-native/pull/28048

Test Plan: Circle CI

Reviewed By: TheSavior

Differential Revision: D19887240

Pulled By: hramos

fbshipit-source-id: a8d553dca0f47a5ab6132a3880830a60a1b28736

.circleci/config.yml

@@ -12,14 +12,14 @@ defaults: &defaults
 #        EXECUTORS
 # -------------------------
 executors:
-  node8:
-    <<: *defaults
-    docker:
-      - image: circleci/node:8
   nodelts:
     <<: *defaults
     docker:
-      - image: circleci/node:lts
+      - image: circleci/node:12
+  nodeprevlts:
+    <<: *defaults
+    docker:
+      - image: circleci/node:10
   reactnativeandroid:
     <<: *defaults
     docker:
@@ -191,7 +191,7 @@ jobs:
     parameters:
         executor:
           type: executor
-          default: node8
+          default: nodelts
         checkout_type:
           type: string
           default: node
@@ -246,7 +246,7 @@ jobs:
   #    JOBS: Analyze Code
   # -------------------------
   analyze_code:
-    executor: node8
+    executor: nodelts
     steps:
       - restore_cache_checkout:
           checkout_type: node
@@ -291,7 +291,7 @@ jobs:
     parameters:
       executor:
         type: executor
-        default: node8
+        default: nodelts
     executor: << parameters.executor >>
     steps:
       - restore_cache_checkout:
@@ -436,7 +436,7 @@ jobs:
           path: ./reports/junit
 
   test_js_e2e:
-    executor: node8
+    executor: nodelts
     steps:
       - restore_cache_checkout:
           checkout_type: node
@@ -575,7 +575,7 @@ jobs:
   # -------------------------
   # Collect JavaScript test coverage
   js_coverage:
-    executor: node8
+    executor: nodelts
     environment:
       - CI_BRANCH: $CIRCLE_BRANCH
       - CI_PULL_REQUEST: $CIRCLE_PULL_REQUEST
@@ -665,8 +665,8 @@ workflows:
             - setup_ios
             - test_js
       - test_js:
-          name: test_js_lts
-          executor: nodelts
+          name: test_js_prev_lts
+          executor: nodeprevlts
           requires:
             - setup_js
       - test_docker: