Refactor changelog parsing and generation

[Gudahtt]

The auto-changelog.js script has been refactoring into various different modules. This was done in preparation for migrating this to a separate repository, where it can be used in our libraries as well.

Functionally this should act mostly the same way, but there have been some changes. It was difficult to make this a pure refactor because of the strategy used to validate the changelog and ensure each addition remained valid. Instead of being updated in-place, the changelog is now parsed upfront and stored as a "Changelog" instance, which is a new class that was written to allow only valid changes. The new changelog is then stringified and completely overwrites the old one.

The parsing had to be much more strict, as any unanticipated content would otherwise be erased unintentionally. This script now also normalizes the formatting of the changelog (though the individual change descriptions are still unformatted).

The changelog stringification now accommodates non-linear releases as well. For example, you can now release v1.0.1 after v2.0.0, and it will be listed in chronological order while also correctly constructing the compare URLs for each release.

Relates to #10752

Manual testing steps:

To update the changelog with unreleased changes:

• Run yarn update-changelog
• See that it puts changes under the "Unreleased" header

To update the changelog for a release candidate:

• Run yarn update-changelog --rc
• See that it puts changes under the header for the current release candidate

[metamaskbot]

Builds ready [50df31f]

• builds: chrome, firefox, opera
• bundle viz: background, ui, inpage, contentscript, ui-libs, bg-libs, phishing-detect
• build viz: Build System
• code coverage: Report
• storybook: Storybook
• all artifacts

Page Load Metrics (656 ± 50 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	48	79	62	8	4
		domContentLoaded	373	827	655	104	50
		load	375	828	656	104	50
		domInteractive	373	826	654	104	50

[metamaskbot]

Builds ready [554d153]

• builds: chrome, firefox, opera
• bundle viz: background, ui, inpage, contentscript, ui-libs, bg-libs, phishing-detect
• build viz: Build System
• code coverage: Report
• storybook: Storybook
• all artifacts

Page Load Metrics (601 ± 69 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	44	81	57	10	5
		domContentLoaded	367	1065	600	145	69
		load	368	1066	601	144	69
		domInteractive	366	1064	600	145	69

[metamaskbot]

Builds ready [459b991]

• builds: chrome, firefox, opera
• bundle viz: background, ui, inpage, contentscript, ui-libs, bg-libs, phishing-detect
• build viz: Build System
• code coverage: Report
• storybook: Storybook
• all artifacts

Page Load Metrics (582 ± 39 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	45	79	58	9	4
		domContentLoaded	404	681	581	82	39
		load	409	682	582	81	39
		domInteractive	403	681	580	82	39

[brad-decker]

Output looks good for both baseline and --rc flag, code looks much cleaner and broken into fairly easy-to-digest pieces. LGTM 👍🏻 Especially like the amount of comments / docblocks to explain what each piece does.