refactor: introduce SSR variable for platform checks

[dhhyi]

PR Type

[x] Feature
[x] Refactoring (no functional changes, no API changes)

What Is the Current Behavior?

For checking if the current Angular app is running in SSR or Browser, the PLATFORM_ID has to be injected and the methods isPlatformBrowser and isPlatformServer have to be used to perform the check. This always requires DI context and is rather verbose.

What Is the New Behavior?

• The customized build sets the variable SSR that can be used for this check.
• Added lint rule that suggests code changes.
• Transformed all occurrences.
• Add onSSREnvironment to jest describe so the SSR variable can be set for testing (default is false)

Does this PR Introduce a Breaking Change?

[ ] Yes
[x] No

Other Information

As the SSR value is now injected into the build process with the webpack DefinePlugin, the values can be used for code minification. When using the usual way with PLATFORM_ID, the chack can only be performed at runtime and all code is ending up in server and client bundles.

Verify this by adding the following code:

    if (!SSR) {
      console.log('browser - QWERTY1234');
    }
    if (SSR) {
      console.log('server - QWERTY1234');
    }

Check where it turns up with (bash):

~$ npm run build
...
~$ grep -ro '\w* - QWERTY1234' dist
dist/server/main.js:server - QWERTY1234
dist/browser/main.e9860fd746f0e9c6.js:browser - QWERTY1234

AB#75426

[shauke]

It seems like a nice improvement but we should introduce it with the next major version and not with a 2.x minor version. At least if there are no further objections.

[dhhyi]

It seems like a nice improvement but we should introduce it with the next major version and not with a 2.x minor version.

Good idea. I'll keep the branch up-to-date until then whenever it has conflicts 😉👍