Add Pagefind incremental indexing

[MoshiMoshiMochi]

What is the purpose of this pull request?

• Documentation update
• Bug fix
• Feature addition or enhancement
• Code maintenance
• DevOps
• Improve developer experience
• Others, please explain:

Overview of changes:
closes #2873
Implemented incremental Pagefind search index

Anything you'd like to highlight/discuss:
The incremental Pagefind search index works in the following manner.

1. If a user updates a page -> Pagefind will re-index that specific page.
2. If a user creates a new page -> Pagefind will index that specific new page.
3. If a user deletes a page -> Pagefind will re-index all pages.

For deleting I couldn't find a way to remove just 1 specific index file from in-memory indexes. Hence, I decided that the remove handler will use indexSiteWithPagefind, meaning that it will reindex the entire site. There might be a better solution out there. But since removing already calls rebuildSourceFiles which takes significantly longer than it takes to reindex the site, I don't think its a big deal. But hey just something to note if possible to improve ig.

Technically this some what tackles #2882 but it does so indirectly as we no longer call indexSiteWithPagefind when serving one-page, instead we call updatePagefindIndex which incrementally indexes pages.

Testing instructions:
Full build: markbind serve -d

1. Serve any markbind site
2. Update any page and save the changes -> Pagefind should only index that one page -> Check to see if the changes are within the search
3. Add any page -> Pagefind should only index that newly added page -> Check to see if the newly create page is searchable by Pagefind
4. Delete any page -> Pagefind should re-index the entire site -> Check to see if the removed page is no longer searchable

One-Page: markbind serve -o

1. Serve any markbind site with just one-page -> Pagefind should index that specific page if it is searchable
2. Navigate through the other pages -> Pagefind should index those pages incrementally

Proposed commit message: (wrap lines at 72 characters)
Add Pagefind incremental indexing

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Checklist: ☑️

• Updated the documentation for feature additions and enhancements
• Added tests for bug fixes or features
• Linked all related issues
• No unrelated changes

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Reviewer checklist:

Indicate the SEMVER impact of the PR:

• Major (when you make incompatible API changes)
• Minor (when you add functionality in a backward compatible manner)
• Patch (when you make backward compatible bug fixes)

At the end of the review, please label the PR with the appropriate label: r.Major, r.Minor, r.Patch.

Breaking change release note preparation (if applicable):

• To be included in the release note for any feature that is made obsolete/breaking

Give a brief explanation note about:

• what was the old feature that was made obsolete
• any replacement feature (if any), and
• how the author should modify his website to migrate from the old feature to the replacement feature (if possible).

[codecov]

Codecov Report

❌ Patch coverage is 84.37500% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.75%. Comparing base (b3b90c8) to head (555d1c3).

Files with missing lines	Patch %	Lines
packages/core/src/Site/SiteGenerationManager.ts	82.45%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2890      +/-   ##
==========================================
+ Coverage   71.35%   71.75%   +0.39%     
==========================================
  Files         133      133              
  Lines        7229     7285      +56     
  Branches     1611     1720     +109     
==========================================
+ Hits         5158     5227      +69     
+ Misses       2065     2052      -13     
  Partials        6        6              

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