refactor(angular, react, vue): add missing test app msg (#28951)

Issue number: N/A

---------

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issue. -->

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## What is the current behavior?
<!-- Please describe the current behavior that you are modifying. -->

The packages, Angular, React, and Vue, will accept any `app_dir`
parameter when passing it to the build script. This can lead to a user
to entering a directory that doesn't exist within `test/apps`. If this
happens, then the build folder will include an incomplete test app.

For example:
1. `./build ng13`
2. This creates a `build/ng13` folder, but the folder only contains the
contents from the `base` folder. This causes it to be incomplete.

## What is the new behavior?
<!-- Please describe the behavior or changes that are being added by
this PR. -->

- Provides a message that the provided app directory doesn't exist.
- Does not create the incomplete app when an invalid app directory is
given.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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## Other information

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screenshots of how the component looks before and after the change. -->

N/A

packages/angular/test/build.sh

@@ -22,6 +22,12 @@ FULL_BASE_DIR="${BASE_DIR}/."
 # The full path to the built application.
 BUILD_APP_DIR="${BUILD_DIR}/${APP_DIR}/"
 
+# Make sure the full app directory exists.
+if [ ! -d $FULL_APP_DIR ]; then
+  echo "Could not find test app: ${FULL_APP_DIR}"
+  exit 1
+fi
+
 # Make the build directory if it does not already exist.
 mkdir -p $BUILD_DIR
 

packages/react/test/build.sh

@@ -22,6 +22,12 @@ FULL_BASE_DIR="${BASE_DIR}/."
 # The full path to the built application.
 BUILD_APP_DIR="${BUILD_DIR}/${APP_DIR}/"
 
+# Make sure the full app directory exists.
+if [ ! -d $FULL_APP_DIR ]; then
+  echo "Could not find test app: ${FULL_APP_DIR}"
+  exit 1
+fi
+
 # Make the build directory if it does not already exist.
 mkdir -p $BUILD_DIR
 

packages/vue/test/build.sh

@@ -22,6 +22,12 @@ FULL_BASE_DIR="${BASE_DIR}/."
 # The full path to the built application.
 BUILD_APP_DIR="${BUILD_DIR}/${APP_DIR}/"
 
+# Make sure the full app directory exists.
+if [ ! -d $FULL_APP_DIR ]; then
+  echo "Could not find test app: ${FULL_APP_DIR}"
+  exit 1
+fi
+
 # Make the build directory if it does not already exist.
 mkdir -p $BUILD_DIR