fix(content-blog): temporarily swallow feed mdxToHtml errors + feed refactor

[slorber]

Motivation

Quick hacky fix for site builds failing due to unability to transform mdx blog posts to RSS/Atom feed HTML content.

The problem is explained here, and not simple to solve properly: #5664

• Fixes Error reported by "useBaseUrl" during construction #5736
• Fixes Site fails to build production site with blog post that uses require after upgrading to beta 7 #5718

Note:

• We try to generate full HTML content when possible, but fail-safe when we fail: the feed entry remains available, it's just that RSS readers won't display the real blog post content. It was the behavior before and is not a big deal
• We swallow the error on purpose: I didn't want to introduce a warning nor a plugin option until we understand better how to fix this problem properly => we may add a warning/plugin option later if it is clear we need this

Also, refactor the feed code a bit to make it easier to understand.

Have you read the Contributing Guidelines on pull requests?

yes

Test Plan

tests + preview / dogfood

Related PRs

PR for blog full feed:

#4330

[netlify]

✔️ [V2]

🔨 Explore the source changes: 111154f

🔍 Inspect the deploy log: https://app.netlify.com/sites/docusaurus-2/deploys/61705780c99dda0007f9cfbf

😎 Browse the preview: https://deploy-preview-5753--docusaurus-2.netlify.app

[github-actions]

⚡️ Lighthouse report for the changes in this PR:

Category	Score
🟠 Performance	71
🟢 Accessibility	98
🟢 Best practices	100
🟢 SEO	100
🟢 PWA	95

Lighthouse ran on https://deploy-preview-5753--docusaurus-2.netlify.app/

[github-actions]

Size Change: +707 B (0%)

Total Size: 844 kB

Filename	Size	Change
website/build/assets/js/main.********.js	425 kB	+701 B (0%)

ℹ️ View Unchanged

Filename	Size	Change
website/.docusaurus/globalData.json	38.1 kB	0 B
website/build/assets/css/styles.********.css	93.8 kB	0 B
website/build/blog/2017/12/14/introducing-docusaurus/index.html	67.7 kB	0 B
website/build/blog/index.html	38.5 kB	0 B
website/build/docs/index.html	45.7 kB	+3 B (0%)
website/build/docs/installation/index.html	53.4 kB	+3 B (0%)
website/build/index.html	31.2 kB	0 B
website/build/tests/docs/index.html	26.6 kB	0 B
website/build/tests/docs/standalone/index.html	23.3 kB	0 B

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