[Android]: Report SDK size as a comment in PRs

[bruno-garcia]

We'd like to start managing the bundle size of the SDK more actively.

For that, we'd like to start taking some numbers during PRs, and with the end goal of posting as a PR comment the bundle size and a diff to main.

Approaches considered and characteristics of them:

Measuring the aar

• Either we do a naive measurement solely of our package without considering dependencies. Or we need to recursively find all dependencies and measure their sizes.
• There are multiple slices on each aar, for each abi.
  • We'd need to compile for a specific one, or peek into the aar to calculate specific architectures.

Measuring the final app

• We can run proguard on the sample app which has heavy use of our features and measure more realistically the "overhead" in bundle size.

Suggested Phases:

• Measure size of sample app
• Post size as a comment to PR
• Add flavor without Sentry and measure size
• Post both to PR the metrics
  • Sizes (like JS bundle on getsentry/sentry) to PR
  • Method count
  • Diff (using JakeWharton/diffuse or Tencent/matrix@master/matrix/matrix-android/matrix-apk-canary)
• Proguard the sample app (both withSentryAndNdk and withoutSentryOrNdk flavors)
• Document size
  • For example: https://pspdfkit.com/guides/android/current/faq/framework-size/
  • Not having Kotlin so kotlin std doesn't affect size

[romtsn]

Some inspiration: firebase/firebase-android-sdk#3011 (comment)

[philipphofmann]

Worth noting that our JavaScript repo already has something like this, see getsentry/sentry-javascript#4993 (comment).

[marandaneto]

Somehow related #1411

[philipphofmann]

We could use https://github.com/JakeWharton/diffuse

Diffuse is a tool for diffing APKs, AABs, AARs, and JARs in a way that aims to provide both a high-level view of what changes along with important detailed output.

[philipphofmann]

The first goal would be to get the output of diffuse and just add it as a comment to the PR.

Example output of diffuse:

          │          compressed           │          uncompressed
          ├───────────┬───────────┬───────┼───────────┬───────────┬────────
 APK      │ old       │ new       │ diff  │ old       │ new       │ diff
──────────┼───────────┼───────────┼───────┼───────────┼───────────┼────────
      dex │ 664.8 KiB │ 664.8 KiB │ -25 B │   1.5 MiB │   1.5 MiB │ -112 B
     arsc │ 201.7 KiB │ 201.7 KiB │   0 B │ 201.6 KiB │ 201.6 KiB │    0 B
 manifest │   1.4 KiB │   1.4 KiB │   0 B │   4.2 KiB │   4.2 KiB │    0 B
      res │ 418.2 KiB │ 418.2 KiB │ -14 B │ 488.3 KiB │ 488.3 KiB │    0 B
    asset │       0 B │       0 B │   0 B │       0 B │       0 B │    0 B
    other │  37.1 KiB │  37.1 KiB │   0 B │  36.3 KiB │  36.3 KiB │    0 B
──────────┼───────────┼───────────┼───────┼───────────┼───────────┼────────
    total │   1.3 MiB │   1.3 MiB │ -39 B │   2.2 MiB │   2.2 MiB │ -112 B