Various changes

[modulovalue]

Hello Steve,
Thank you for porting perfect freehand to dart.
I was curious what kind of dart and flutter code someone with programming experience, but new to Dart, would write.

You said on twitter that you are open to feedback, so here are some suggestions.

The most important changes in this PR are the following:

• extracted dart only logic into its own package (FYI you could use dart instead of typescript for deploying a js version of perfect freehand, see: https://dart.dev/tools/dart2js)
• replaced streamcontrollers with setState (they are not needed in this case, setState is enough to notify the UI to repaint)
• made some models const-able (the linter is able to highlight constructor calls that can be made constant. This will be more efficient in Dart as such models will only have to be allocated once.)
• removed the set invocation from some setState calls which look like closures but aren't closures (closures don't need an arrow (abc) {} / function expressions don't need curly braces (abc) => ...

Some of the more subjective changes are:

• removed newlines for clarity
• added trailing commas to help dartfmt
• replaced ternary operators with ifelses for clarity
• sorted methods in the main widget topologically which is more idiomatic in dart than a reverse topological sort.

FYI: Flutter supports reading out various information from pressure sensitive input devices such as the Apple Pen on iPads.

Thanks again :)

[modulovalue]

I'm not going to be able to merge his PR [...]

No problem!

[steveruizok]

But seriously, thanks! I've moved over most of your changes into the main branch. With the exception of removing line newlines—I think our eyes might work a bit differently. ;)