[FEATURE] Add support for Ember 4.8

We were previously using 4.6. We'll aim to keep this up to date going
forward. Here, update the dependency and then address two safety issues
it caught on either 4.7 or 4.8 but did not back on 4.6.

package.json

@@ -157,7 +157,7 @@
     "simple-dom": "^1.4.0",
     "testem": "^3.8.0",
     "testem-failure-only-reporter": "^1.0.0",
-    "typescript": "~4.6.4"
+    "typescript": "~4.8.3"
   },
   "peerDependencies": {
     "@glimmer/component": "^1.1.2"

packages/@ember/-internals/glimmer/lib/helper.ts

@@ -105,7 +105,10 @@ class Helper extends FrameworkObject {
   static isHelperFactory = true;
   static [IS_CLASSIC_HELPER] = true;
 
-  [RECOMPUTE_TAG]: DirtyableTag;
+  // SAFETY: this is initialized in `init`, rather than `constructor`. It is
+  // safe to `declare` like this *if and only if* nothing uses the constructor
+  // directly in this class, since nothing else can run before `init`.
+  declare [RECOMPUTE_TAG]: DirtyableTag;
 
   init(properties: object | undefined) {
     super.init(properties);

packages/@ember/-internals/metal/lib/libraries.ts

@@ -86,7 +86,7 @@ if (DEBUG) {
     let nameLengths = libs.map((item) => get(item, 'name.length'));
     assert(
       'nameLengths is number array',
-      nameLengths instanceof Array && nameLengths.every((n) => typeof n === 'number')
+      nameLengths instanceof Array && nameLengths.every((n): n is number => typeof n === 'number')
     );
     let maxNameLength = Math.max.apply(null, nameLengths);
 

yarn.lock

@@ -10239,10 +10239,10 @@ typescript-memoize@^1.0.0-alpha.3, typescript-memoize@^1.0.1:
   resolved "https://registry.yarnpkg.com/typescript-memoize/-/typescript-memoize-1.1.0.tgz#4a8f512d06fc995167c703a3592219901db8bc79"
   integrity sha512-LQPKVXK8QrBBkL/zclE6YgSWn0I8ew5m0Lf+XL00IwMhlotqRLlzHV+BRrljVQIc+NohUAuQP7mg4HQwrx5Xbg==
 
-typescript@~4.6.4:
-  version "4.6.4"
-  resolved "https://registry.yarnpkg.com/typescript/-/typescript-4.6.4.tgz#caa78bbc3a59e6a5c510d35703f6a09877ce45e9"
-  integrity sha512-9ia/jWHIEbo49HfjrLGfKbZSuWo9iTMwXO+Ca3pRsSpbsMbc7/IU8NKdCZVRRBafVPGnoJeFL76ZOAA84I9fEg==
+typescript@~4.8.3:
+  version "4.8.3"
+  resolved "https://registry.yarnpkg.com/typescript/-/typescript-4.8.3.tgz#d59344522c4bc464a65a730ac695007fdb66dd88"
+  integrity sha512-goMHfm00nWPa8UvR/CPSvykqf6dVV8x/dp0c5mFTMTIu0u0FlGWRioyy7Nn0PGAdHxpJZnuO/ut+PpQ8UiHAig==
 
 uc.micro@^1.0.0, uc.micro@^1.0.1, uc.micro@^1.0.5:
   version "1.0.6"