Blocks: Treat RangeControl value as numeric

[aduth]

This pull request seeks to update RangeControl in line with other block inspector controls to pass through the updated value on onChange instead of the original event, and in doing so treat the updated value as numeric. Since RangeControl is used for assigning numeric values, it was easy to overlook and assigning event.target.value would assign a string value, resulting in warnings:

parser.js:140 Expected attribute "columns" of type number for block type "core/gallery" but received string.

See: #1905

Testing instructions:

Verify there are no regressions or console warnings in changing...

• Gallery columns
• Latest posts columns
• Text columns columns

Ensure unit tests pass:

npm test

[codecov]

Codecov Report

Merging #2339 into master will increase coverage by 0.04%.
The diff coverage is 25%.

@@            Coverage Diff             @@
##           master    #2339      +/-   ##
==========================================
+ Coverage   24.69%   24.74%   +0.04%     
==========================================
  Files         152      152              
  Lines        4738     4745       +7     
  Branches      799      800       +1     
==========================================
+ Hits         1170     1174       +4     
- Misses       3014     3016       +2     
- Partials      554      555       +1

Impacted Files	Coverage Δ
blocks/library/gallery/index.js	25% <0%> (ø)	⬆️
blocks/library/latest-posts/index.js	10% <0%> (ø)	⬆️
blocks/library/text-columns/index.js	33.33% <0%> (ø)	⬆️
blocks/inspector-controls/range-control/index.js	100% <100%> (+100%)	⬆️
editor/sidebar/post-status/index.js	0% <0%> (ø)	⬆️
blocks/inspector-controls/base-control/index.js	100% <0%> (+100%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ca1eeda...961c98d. Read the comment docs.