refactor(formatter): Use slice to store content

[MichaReiser]

Summary

This PR changes the Content type alias for FormatElement from Box<FormatElement> to Box<[FormatElement]>.

The main motivation behind this is that VecBuffer always allocates a new vector even if only one element was written. Instead of discarding this vector and then boxing the element this PR uses vec.into_boxed_slice that avoids the additional allocation.

Dhat numbers:

Formatted
	Memory
		Current Blocks: 63751 -> 57091
		Current Bytes: 6.07 MB -> 5.28 MB
		Max Blocks: 63793 -> 57136
		Max Bytes: 6.08 MB -> 5.29 MB
		Total Blocks: 329404 -> 328939
		Total Bytes: 23.83 MB -> 24.87 MB
Printed (no changes, as unaffected)
	Memory
		Current Blocks: 20139
		Current Bytes: 2.75 MB
		Max Blocks: 57098
		Max Bytes: 6.57 MB
		Total Blocks: 5472
		Total Bytes: 2.58 MB

Test Plan

This PR isn't adding any new functionality.

Performance

group                                    main                                    slice
-----                                    ----                                    -----
formatter/checker.ts                     1.02    221.4±1.87ms    11.7 MB/sec     1.00    216.1±3.17ms    12.0 MB/sec
formatter/compiler.js                    1.05    141.2±8.11ms     7.4 MB/sec     1.00    135.0±1.14ms     7.8 MB/sec
formatter/d3.min.js                      1.00    110.8±3.41ms     2.4 MB/sec     1.03   114.2±19.37ms     2.3 MB/sec
formatter/dojo.js                        1.01      7.5±0.03ms     9.2 MB/sec     1.00      7.4±0.02ms     9.3 MB/sec
formatter/ios.d.ts                       1.03    150.9±0.95ms    12.4 MB/sec     1.00    147.0±5.47ms    12.7 MB/sec
formatter/jquery.min.js                  1.00     29.1±0.07ms     2.8 MB/sec     1.00     29.0±0.15ms     2.8 MB/sec
formatter/math.js                        1.00    229.5±1.36ms     2.8 MB/sec     1.01    232.9±1.46ms     2.8 MB/sec
formatter/parser.ts                      1.07      5.0±0.03ms     9.6 MB/sec     1.00      4.7±0.09ms    10.2 MB/sec
formatter/pixi.min.js                    1.02    126.0±2.88ms     3.5 MB/sec     1.00    124.0±2.83ms     3.5 MB/sec
formatter/react-dom.production.min.js    1.00     35.0±1.02ms     3.3 MB/sec     1.02     35.6±0.59ms     3.2 MB/sec
formatter/react.production.min.js        1.04  1867.1±182.20µs     3.3 MB/sec    1.00  1791.8±17.46µs     3.4 MB/sec
formatter/router.ts                      1.02      3.6±0.01ms    16.3 MB/sec     1.00      3.6±0.01ms    16.5 MB/sec
formatter/tex-chtml-full.js              1.03    300.3±1.71ms     3.0 MB/sec     1.00    292.9±1.57ms     3.1 MB/sec
formatter/three.min.js                   1.02    146.4±2.54ms     4.0 MB/sec     1.00    143.0±1.22ms     4.1 MB/sec
formatter/typescript.js                  1.01   901.4±14.89ms    10.5 MB/sec     1.00   895.9±17.75ms    10.6 MB/sec
formatter/vue.global.prod.js             1.00     46.0±0.16ms     2.6 MB/sec     1.00     45.8±0.54ms     2.6 MB/sec

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Latest commit:	15f9c45
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Branch Preview URL:	https://refactor-content-to-slice.tools-8rn.pages.dev

View logs

[github-actions]

Playground for commit 1233edb

[github-actions]

Parser conformance results on ubuntu-latest

js/262

Test result	main count	This PR count	Difference
Total	45878	45878	0
Passed	44938	44938	0
Failed	940	940	0
Panics	0	0	0
Coverage	97.95%	97.95%	0.00%

jsx/babel

Test result	main count	This PR count	Difference
Total	39	39	0
Passed	36	36	0
Failed	3	3	0
Panics	0	0	0
Coverage	92.31%	92.31%	0.00%

symbols/microsoft

Test result	main count	This PR count	Difference
Total	5946	5946	0
Passed	388	388	0
Failed	5558	5558	0
Panics	0	0	0
Coverage	6.53%	6.53%	0.00%

ts/babel

Test result	main count	This PR count	Difference
Total	588	588	0
Passed	519	519	0
Failed	69	69	0
Panics	0	0	0
Coverage	88.27%	88.27%	0.00%

ts/microsoft

Test result	main count	This PR count	Difference
Total	16257	16257	0
Passed	12393	12393	0
Failed	3864	3864	0
Panics	0	0	0
Coverage	76.23%	76.23%	0.00%