Dont use kotlin reflection (#1544)

[kzotin]

Kotlin reflection is super slow on some old devices (~20seconds on cold start, see #1544 ), which is a blocker for us after migrating from realm-java to kotlin.

We've got such device, and fix was verified there

[cla-bot]

Realm welcomes all contributions! The only requirement we have is that, like many other projects, we need to have a Contributor License Agreement (CLA) in place before we can accept any external code. Our own CLA is a modified version of the Apache Software Foundation’s CLA. Our records show that CLA has not been signed by @kzotin. Please submit your CLA electronically using our Google form so we can accept your submissions. After signing the CLA you can recheck this PR with a @cla-bot check comment. The GitHub usernames you file there will need to match that of your Pull Requests. If you have any questions or cannot file the CLA electronically, make a comment here and we will be happy to help you out.

[kzotin]

PS. I've submitted the CLA form yesterday

[stavfx]

@cla-bot check

[cla-bot]

Realm welcomes all contributions! The only requirement we have is that, like many other projects, we need to have a Contributor License Agreement (CLA) in place before we can accept any external code. Our own CLA is a modified version of the Apache Software Foundation’s CLA. Our records show that CLA has not been signed by @kzotin. Please submit your CLA electronically using our Google form so we can accept your submissions. After signing the CLA you can recheck this PR with a @cla-bot check comment. The GitHub usernames you file there will need to match that of your Pull Requests. If you have any questions or cannot file the CLA electronically, make a comment here and we will be happy to help you out.

[cla-bot]

The cla-bot has been summoned, and re-checked this pull request!

[stavfx]

@kzotin I think you signed the form as "@kzotin" instead of "kzotin" and that's why the cla-bot is still failing

[MrJohn10]

@cla-bot check

[cla-bot]

The cla-bot has been summoned, and re-checked this pull request!

[clementetb]

Would you mind adding a changelog entry to the PR?

[kzotin]

Updated the changelog