🔥 Remove flutter as a submodule (flutter#9307)

_Description of what this PR is changing or adding, and why:_
The PR removes the `flutter` repo as a submodule to avoid conflicts when
building the website on different platforms. It was first introduced in
flutter#1257 but with no explanation so we cannot track back what's the
purpose, but removing this should not cause difficulties in maintaining
the website.

### Additional info

- The build process is slower than the previous one because the checkout
step needs an extra 3~5 minutes, depending on the network condition. See
[now](https://github.com/flutter/website/actions/runs/5985413443/job/16237673762?pr=9307)
and
[previous](https://github.com/flutter/website/actions/runs/5983398408/job/16237673076?pr=9298)
checks.

_Issues fixed (partially) by this PR (if any):_
- flutter#6201
- flutter#6443
- flutter#8272

## Presubmit checklist

- [x] This PR doesn’t contain automatically generated corrections
(Grammarly or similar).
- [x] This PR follows the [Google Developer Documentation Style
Guidelines](https://developers.google.com/style) — for example, it
doesn’t use _i.e._ or _e.g._, and it avoids _I_ and _we_ (first person).
- [x] This PR uses [semantic line
breaks](https://github.com/dart-lang/site-shared/blob/main/doc/writing-for-dart-and-flutter-websites.md#semantic-line-breaks)
of 80 characters or fewer.

---------

Co-authored-by: Anthony Sansone <atsansone@users.noreply.github.com>
Co-authored-by: Parker Lougheed <parlough@gmail.com>

.dockerignore

@@ -5,4 +5,5 @@ CONTRIBUTING.md
 docker-compose.yml
 LICENSE
 node_modules/
-README.md
+README.md
+flutter/

.gitattributes

@@ -3,3 +3,11 @@
 
 # Allow dart files in examples/ to be detectable
 examples/**/*.dart -linguist-documentation
+
+# Handles files and normalization
+*       text=auto
+*.sh    text eol=lf
+*.bat   text eol=crlf
+*.dart  text eol=lf
+dart    text eol=lf
+flutter text eol=lf

.gitignore

@@ -10,6 +10,7 @@ _site
 *.swp
 build
 node_modules
+flutter/
 
 # Dart and Flutter, build related
 .dart_tool

.gitmodules

@@ -2,10 +2,6 @@
 	path = site-shared
 	url = https://github.com/dart-lang/site-shared
 	branch = main
-[submodule "flutter"]
-	path = flutter
-	url = https://github.com/flutter/flutter
-	branch = stable
 [submodule "examples/codelabs"]
 	path = examples/codelabs
 	url = https://github.com/flutter/codelabs

Dockerfile

@@ -25,29 +25,16 @@ WORKDIR /app
 # or run `git submodule update --init --recursive` after cloning.
 FROM base AS flutter
 
-# This Flutter install uses/requires the local ./flutter submodule
-COPY ./flutter ./flutter
 COPY ./site-shared ./site-shared
 COPY pubspec.yaml ./
 
-ARG FLUTTER_BUILD_BRANCH
+ARG FLUTTER_BUILD_BRANCH=stable
 ENV FLUTTER_BUILD_BRANCH=$FLUTTER_BUILD_BRANCH
 ENV FLUTTER_ROOT=flutter
 ENV FLUTTER_BIN=flutter/bin
 ENV PATH="/app/flutter/bin:$PATH"
 
-# Used if wanting to build the container with a different branch, this
-# would change the current branch of and update the mirrored submodule
-# e.g. `make build FLUTTER_BUILD_BRANCH=beta`
-# This is not to be confused with the $FLUTTER_TEST_BRANCH
-RUN if test -n "$FLUTTER_BUILD_BRANCH" -a "$FLUTTER_BUILD_BRANCH" != "stable" ; then \
-      cd flutter && \
-      git fetch && \
-      git remote set-branches origin "$FLUTTER_BUILD_BRANCH" && \
-      git fetch --depth 1 origin "$FLUTTER_BUILD_BRANCH" && \
-      git checkout "$FLUTTER_BUILD_BRANCH" -- && \
-      git pull; \
-    fi
+RUN git clone --branch $FLUTTER_BUILD_BRANCH --single-branch https://github.com/flutter/flutter ./flutter
 
 # Set up Flutter
 # NOTE You will get a warning "Woah! You appear to be trying to run flutter as root."

README.md

@@ -102,16 +102,8 @@ Install the following tools, if you don't have them already:
 > The GitHub documentation has general help on
 > [forking][] and [cloning][] repos.
 
-If you are working in the Windows desktop environment,
-make sure you have Git `autocrlf` set to `input`
-**before** initializing the submodules.
-This ensures that line endings are handled correctly
-_before_ any Bash scripts are executed within the submodules.
-See [issue 6201][] for details.
-
 [cloning]: https://help.github.com/articles/cloning-a-repository
 [forking]: https://docs.github.com/en/get-started/quickstart/fork-a-repo
-[issue 6201]: https://github.com/flutter/website/issues/6201
 
 If you're outside of the Flutter organization, 
 we recommend you **create a fork** of the repo under your own account, 
@@ -127,7 +119,7 @@ _choose one_ of the following submodule-cloning techniques:
   ```
 
   OR
-  
+
 - If you've already cloned the repo without its submodule, 
   then run this command from the repo root:<br>
   ```bash
@@ -148,7 +140,7 @@ _choose one_ of the following submodule-cloning techniques:
    ```bash
    $ git checkout -b <BRANCH_NAME>
    ```
-   
+
 1. If the Docker Desktop application isn't already running,
    start it. Look at its status icon: 
    if it has an exclamation point (`!`),
@@ -196,7 +188,7 @@ _choose one_ of the following submodule-cloning techniques:
    ```bash
    $ make down
    ```
-   
+
 > **Tip:** To find additional commands, read the [`Makefile`][]. 
 > For example, if you need to debug the Docker infrastructure, 
 > you can run `make debug`.