Moved to using rollup directly instead of tslib-cli

[TobiasBerg]

So I wanted to fix the IE11 issue, but when I started working on it the tslib-cli kinda got in the way.

Not trying to step on any toes with this PR, but hope this is something you would like to merge. Any feedback is greatly appreciated.
When merged I would like to work on the IE11 issue and the other bug report if needed.

I have simplified the build setup a ton by removing tslib-cli and just using rollup directly.
The reasons for removing it are as follows:

• tslib-cli was not being updated in this repo and it looks like it's undergone a complete rewrite so upgrading is not trivial
• It makes it harder for newcomers to understand how the build is set up
• It uses a ton of dependencies
• Makes it harder to work on this repo
• tslib-cli actually confused me a lot as I thought it had something to to with tslib, which it does not

This produces the same output as before so should not be a breaking change.
A lot of the quality of life stuff in the build like outputting filesizes are gone, I am going for simplicity here, but if you would like some it back, let me know and I can add it in the rollup build.

Looking forward to your feedback. This is my first real OSS contribution, so please don't be too hard on me 😁

[avoidwork]

hi, if it works the same for everyone i think this is fine.