use destructuring syntax for computed props in v2 mode - fixes #1069

[Rich-Harris]

To prevent confusing ambiguity, this doesn't support props: state => state — that can wait for v2.

[codecov-io]

Codecov Report

Merging #1345 into master will decrease coverage by 0.06%.
The diff coverage is 80%.

@@            Coverage Diff             @@
##           master    #1345      +/-   ##
==========================================
- Coverage   91.76%   91.69%   -0.07%     
==========================================
  Files         125      125              
  Lines        4515     4526      +11     
  Branches     1432     1435       +3     
==========================================
+ Hits         4143     4150       +7     
- Misses        149      151       +2     
- Partials      223      225       +2

Impacted Files	Coverage Δ
src/generators/Generator.ts	96.7% <100%> (+0.01%)	⬆️
src/generators/dom/index.ts	95.8% <100%> (+0.05%)	⬆️
src/validate/index.ts	90% <100%> (+0.2%)	⬆️
src/validate/js/propValidators/computed.ts	87.5% <60%> (-12.5%)	⬇️

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