Cache parsed path mapping patterns (#44078)

* Cache parsed path mapping patterns

If a project has many of them (e.g. 1800), parsing the patterns
repeatedly can take up a lot of time.

* Move cache to ConfigFileSpecs

* Inline constants

* Simplify cache access

src/compiler/commandLineParser.ts

@@ -2533,6 +2533,7 @@ namespace ts {
                 validatedFilesSpec: filter(filesSpecs, isString),
                 validatedIncludeSpecs,
                 validatedExcludeSpecs,
+                pathPatterns: undefined, // Initialized on first use
             };
         }