default to accessors: false

[Rich-Harris]

Implements the accessors option as described in #2144 and sets the default to false. It makes me a tiny bit nervous that the default is to have such different behaviour for export let and export function, partly because it'll be a challenge to document, but it does seem weird if the default behaviour is to bloat up people's bundles.

[Conduitry]

What's the interaction between the accessors compiler option and the component option with this?

[codecov-io]

Codecov Report

Merging #2242 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2242   +/-   ##
=======================================
  Coverage   91.83%   91.83%           
=======================================
  Files           1        1           
  Lines          49       49           
=======================================
  Hits           45       45           
  Misses          4        4

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[Rich-Harris]

Component options override compiler options (which default to false normally but true for custom elements where it's generally necessary)

[Conduitry]

And also I guess do we want to expose flush in some way if no accessors becomes the default? We're losing the ability to synchronously update a component.

[Rich-Harris]

Is there a situation where it's necessary to update a component synchronously (as opposed to $set(...) followed by await tick(), which has the same result as far as the user is concerned)? I'm inclined to file it under YAGNI until proven otherwise

[Conduitry]

I'm fine with YAGNIing it, just wanted to mention it. 👍