Multiple assets emit different content to the same filename error for assets with persistent cache

# 🐞 Bug report

### Command (mark with an `x`)

- [ ] new
- [x] build
- [x] serve
- [ ] test
- [ ] e2e
- [ ] generate
- [ ] add
- [ ] update
- [ ] lint
- [ ] extract-i18n
- [ ] run
- [ ] config
- [ ] help
- [ ] version
- [ ] doc

### Is this a regression?

No

### Description

This issue is a continuation for the https://github.com/angular/angular-cli/issues/12186. The fix, introduced for that issue, does not correctly work when using webpack 5 persistent cache.

The problem comes from the fact that when you have multiple assets with the same name, but different folder, CLI emits the first visited asset to the root of fs(disregarding it's folder path), while emiting subsequent assets with this name to their corresponding folders.

To do that Angular CLI keeps track of the emitted(visited) files in-memory, and it does not work when part of the compilation was restored from file system cache. This makes it so that CLI does not realise that a certain svg file was previously emited to the root of the fs, which in turn may lead to the emition of a different svg file(with the same name, but different content) to the same place in the root of the fs, triggering webpack emit conflict error.

## 🔬 Minimal Reproduction

1. Enable webpack 5 persistent cache feature
2. Make sure the cache is clear
3. Create a project with 2 different SVG assets with the same name, but place them in two different folders
4. Import one of this images somewhere in the code of the project
5. Run ng build. The svg is emitted to the root of fs, and is cached
6. Change the code to import second image right before the first one
7. Run ng build again. CLI will try to emit the second svg to the root of fs, but there is already the first svg retrieved from the cache there.
8. You should see the webpack emit conflict error.

## 🔥 Exception or Error

Error: Conflict: Multiple assets emit different content to the same filename empty.svg

## 🌍 Your Environment

Angular CLI: 12.2.0

Node: 14.17.3

Package Manager: npm 6.14.13

OS: darwin x64


Angular: 12.2.0

... animations, cdk, cli, common, compiler, compiler-cli, core

... forms, platform-browser, platform-browser-dynamic, router

Package                         Version

---------------------------------------------------------

@angular-devkit/architect       0.1202.0

@angular-devkit/build-angular   12.2.0

@angular-devkit/core            12.2.0

@angular-devkit/schematics      12.2.0

@schematics/angular             12.2.0

rxjs                            6.6.7

typescript                      4.2.4

webpack                         5.47.1

Beginne damit, das Problem mit `ng build` und dem persistenten Cache von webpack 5 zu reproduzieren: Verwende zwei SVG-Assets mit demselben Dateinamen in verschiedenen Ordnern und ändere dann ihre Importreihenfolge zwischen den Builds. Verfolge, wie zwischengespeicherte und neu besuchte Assets ausgegeben werden. Als erledigt gilt die Aufgabe, wenn wiederholte Builds nicht mehr unterschiedliche Inhalte unter demselben Dateinamen ausgeben oder den webpack-Konfliktfehler auslösen.

Vom Indexierungsmodell aus dem Issue-Text verfasst.