Reorder codebase in SQLite registry

[chilagrow]

Description

Closes #{issue_number}.

Switch the order of code so that sqlite registry has below order

func ExportedAFunc() ...

func unexportedAFunc() ...

func ExportedBFunc() ...

func unexportedbFunc() ..

Readiness checklist

• I added/updated unit tests (and they pass).
• I added/updated integration/compatibility tests (and they pass).
• I added/updated comments and checked rendering.
• I made spot refactorings.
• I updated user documentation.
• I ran task all, and it passed.
• I ensured that PR title is good enough for the changelog.
• (for maintainers only) I set Reviewers (@FerretDB/core), Milestone (Next), Labels, Project and project's Sprint fields.
• I marked all done items in this checklist.

[codecov]

Codecov Report

Merging #3382 (4b08bd5) into main (f98a6f6) will decrease coverage by 6.21%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #3382      +/-   ##
==========================================
- Coverage   74.25%   68.04%   -6.21%     
==========================================
  Files         414      414              
  Lines       25356    25356              
==========================================
- Hits        18827    17254    -1573     
- Misses       5441     6927    +1486     
- Partials     1088     1175      +87     

Files Changed	Coverage
internal/backends/sqlite/metadata/registry.go	100.00%

Flag	Coverage Δ
hana-1	?
hana-2	?
hana-3	?
integration	64.37% <72.72%> (-6.84%)	⬇️
mongodb-1	4.76% <0.00%> (ø)
pg-1	43.85% <0.00%> (ø)
pg-2	43.58% <0.00%> (ø)
pg-3	?
pushdown-false	50.67% <72.72%> (-5.73%)	⬇️
pushdown-true	64.37% <72.72%> (-6.84%)	⬇️
sqlite-1	42.71% <72.72%> (-0.10%)	⬇️
sqlite-2	42.21% <72.72%> (-0.01%)	⬇️
sqlite-3	?
unit	23.39% <100.00%> (-0.03%)	⬇️

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[rumyantseva]

Thanks a lot! More consistency and easier to navigate :)