Cache micromatch in SearchSource globsToMatcher

I was profiling some Jest runs at Airbnb and noticed that on my
MacBook Pro, we can spend over 2 seconds at Jest startup time in
SearchSource getTestPaths. I believe that this will grow as the size
of the codebase increases.

Looking at the call stacks, it appears to be calling micromatch
repeatedly, which calls picomatch, which builds a regex out of the
globs. It seems that the parsing and regex building also triggers the
garbage collector frequently.

Upon testing, I noticed that the globs don't actually change between
these calls, so we can safe a bunch of work by making a micromatch
matcher and reusing that function if the globs haven't changed. In my
basic testing, it is always called with the same set of globs, so I
went with a very simple last-used memoization instead of a more robust
caching solution.

In my profiling of this change locally, this brings down the time of
startRun from about 2000ms to about 200ms.

CHANGELOG.md

@@ -22,6 +22,8 @@
 
 ### Performance
 
+- `[jest-core]` Cache micromatch in SearchSource globsToMatcher
+
 ## 26.0.1
 
 ### Fixes

packages/jest-core/src/SearchSource.ts

@@ -37,8 +37,57 @@ export type TestSelectionConfig = {
   watch?: boolean;
 };
 
-const globsToMatcher = (globs: Array<Config.Glob>) => (path: Config.Path) =>
-  micromatch([replacePathSepForGlob(path)], globs, {dot: true}).length > 0;
+const globsMatchers = new Map<
+  string,
+  {
+    isMatch: (str: string) => boolean;
+    negated: boolean;
+  }
+>();
+
+const globsToMatcher = (globs: Array<Config.Glob>) => {
+  const matchers = globs.map(glob => {
+    if (!globsMatchers.has(glob)) {
+      const state = micromatch.scan(glob, {dot: true});
+      const matcher = {
+        isMatch: micromatch.matcher(glob, {dot: true}),
+        negated: state.negated,
+      };
+      globsMatchers.set(glob, matcher);
+    }
+    return globsMatchers.get(glob);
+  });
+
+  return (path: Config.Path) => {
+    const omit = new Set();
+    const keep = new Set();
+    let negatives = 0;
+    const replacedPath = replacePathSepForGlob(path);
+
+    for (let i = 0; i < matchers.length; i++) {
+      const matcher = matchers[i];
+      if (!matcher) continue;
+      const {isMatch, negated} = matcher;
+      if (negated) negatives++;
+
+      const matched = isMatch(replacedPath);
+
+      const match = negated ? !matched : matched;
+      if (!match) continue;
+
+      if (negated) {
+        omit.add(replacedPath);
+      } else {
+        omit.delete(replacedPath);
+        keep.add(replacedPath);
+      }
+    }
+
+    const result = negatives === matchers.length ? [replacedPath] : [...keep];
+
+    return result.some(item => !omit.has(item));
+  };
+};
 
 const regexToMatcher = (testRegex: Config.ProjectConfig['testRegex']) => (
   path: Config.Path,