With this change we reduce the amount of IO operations. This is especially a huge factor in windows since IO ops are slower.
With this change mainly we cache `existsSync` and `readFileSync` calls
Here's the results
Before
```
//packages/language-service/test:test
INFO: Elapsed time: 258.755s, Critical Path: 253.91s
```
After
```
//packages/language-service/test:test
INFO: Elapsed time: 66.403s, Critical Path: 63.13s
```
PR Close#30585
The 2.6 version of TypeScript's `resolveModuleName` started to
require paths passed to be separated by '/' instead of being
able to handle '\'.
`ngc` and `ng` already do this transformation.
Fixes: #21811
PR Close#21812
Alan
Chuck Jazdzewski