🐞 Bug report

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Is this a regression?

We did not have to use the assets before as on earlier versions this also worked using fileReplacements, and that worked correctly in both ng serve and ng build. This sounds a little like #16670

Description

When using the assets key in the angular.json file, and having a rule that overlaps:

              "assets": [
                "src/favicon.ico",
                "src/assets",
                {
                  "input": "src/assets-replace",
                  "output": "/assets",
                  "glob": "**/*"
                }
              ]

The files from src/assets-replace will overwite the files in src/assets when using ng build, but it does not when using ng serve.

We use this functionality to have different themes of our own app. We use a different configuration for each theme, and have files with the same filename to replace the original logo, like the logo. This not working makes it a little hard to test whether theme changes work correctly.

🔬 Minimal Reproduction

• Change angular.json, see assets example above.
• Add an image.png in your assets folder, and display/show it in a component
• Add an assets-replace folder in your src folder and put another image.png in it
• Execute ng serve and see that it will display the image from src/assets
• Execute ng build and see that it will display the image from src/assets-replace

Example repro repo: https://github.com/jerbob92/angular-cli-assets-overwrite-bug

🌍 Your Environment

Angular CLI: 10.1.7
Node: 12.19.0
OS: linux x64

Angular: 10.1.6
... animations, common, compiler, compiler-cli, core, forms
... platform-browser, platform-browser-dynamic, router
Ivy Workspace: Yes

Package                         Version
---------------------------------------------------------
@angular-devkit/architect       0.1001.7
@angular-devkit/build-angular   0.1001.7
@angular-devkit/core            10.1.7
@angular-devkit/schematics      10.1.7
@angular/cli                    10.1.7
@schematics/angular             10.1.7
@schematics/update              0.1001.7
rxjs                            6.6.3
typescript                      4.0.3