Add ability for libraries actions to report changes in memory usage introduced by a PR

Changes in the flash and dynamic memory for global variables usage of an example sketch are determined during the pull request build by the compile-examples action. The action displays the memory usage data in the log and also saves it to a JSON formatted file.

The actions/upload-artifact action may be used to create a workflow artifact containing the memory usage data files.

The newly added arduino/actions/libraries/report-size-deltas action may be used to provide a table summarizing the memory usage changes as a comment in the pull request thread.

Author: per1234

Dockerfile

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+FROM python:3-slim AS build-env
+ADD . /app
+WORKDIR /app
+
+FROM gcr.io/distroless/python3
+COPY --from=build-env /app /app
+WORKDIR /app
+CMD ["/app/reportsizedeltas.py"]

README.md

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+# libraries/report-size-deltas action
+
+This action comments on the pull request with a report on the change in memory usage of an example sketch. This should be run from a [scheduled workflow](https://help.github.com/en/actions/reference/workflow-syntax-for-github-actions#onschedule).
+
+## Inputs
+
+### `size-deltas-reports-artifact-name`
+
+Name of the workflow artifact that contains the memory usage data, as specified to the actions/upload-artifact action via the name argument
+
+### `github-token`
+
+GitHub access token used to comment the memory usage comparison results to the PR thread. Default [`GITHUB_TOKEN`](https://help.github.com/en/actions/configuring-and-managing-workflows/authenticating-with-the-github_token).
+
+## Example usage
+
+```yaml
+on:
+  schedule:
+    - cron:  '*/5 * * * *'
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: arduino/actions/libraries/report-size-deltas@master
+```

action.yml

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+name: 'Arduino Libraries - Report Size Deltas'
+description: 'Comments on the pull request with a report on the change in memory usage of an example sketch'
+inputs:
+  size-deltas-reports-artifact-name:
+    description: 'Name of the workflow artifact that contains the memory usage data, as specified to the actions/upload-artifact action via the name argument'
+    default: 'size-deltas-reports'
+  github-token:
+    description: 'GitHub access token used to comment the memory usage comparison results to the PR thread'
+    default: ${{ github.token }}
+runs:
+  using: 'docker'
+  image: 'Dockerfile'

reportsizedeltas.py

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+{
+  "fqbn": "adafruit:samd:adafruit_feather_m0",
+  "sketch": "examples/ConnectionHandlerDemo",
+  "previous_flash": 10580,
+  "flash": 10580,
+  "flash_delta": 0,
+  "previous_ram": "N/A",
+  "ram": "N/A",
+  "ram_delta": "N/A"
+}

tests/data/size-deltas-reports/adafruit-samd-adafruit_feather_m0.json

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+{
+  "fqbn": "arduino:samd:mkrgsm1400",
+  "sketch": "examples/ConnectionHandlerDemo",
+  "previous_flash": "N/A",
+  "flash": 51636,
+  "flash_delta": "N/A",
+  "previous_ram": "N/A",
+  "ram": 5104,
+  "ram_delta": "N/A"
+}

tests/data/size-deltas-reports/arduino-samd-mkrgsm1400.json

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+{
+  "fqbn": "arduino:samd:mkrnb1500",
+  "sketch": "examples/ConnectionHandlerDemo",
+  "previous_flash": 50964,
+  "flash": 50940,
+  "flash_delta": -24,
+  "previous_ram": 5068,
+  "ram": 5068,
+  "ram_delta": 0
+}

tests/data/size-deltas-reports/arduino-samd-mkrnb1500.json

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+{
+  "fqbn": "esp8266:esp8266:huzzah",
+  "sketch": "examples/ConnectionHandlerDemo",
+  "previous_flash": 274588,
+  "flash": 274620,
+  "flash_delta": 32,
+  "previous_ram": 27480,
+  "ram": 27496,
+  "ram_delta": 16
+}