Merge Text and RichText

[hackerwins]

What this PR does / why we need it:

Merge Text and RichText

Which issue(s) this PR fixes:

Address #435

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Additional documentation:

Checklist:

• Added relevant tests or not required
• Didn't break anything

[codecov]

Codecov Report

Merging #438 (de089ac) into main (7f7ea60) will decrease coverage by 0.63%.
The diff coverage is 75.43%.

@@            Coverage Diff             @@
##             main     #438      +/-   ##
==========================================
- Coverage   46.96%   46.32%   -0.64%     
==========================================
  Files          71       70       -1     
  Lines        5913     5735     -178     
==========================================
- Hits         2777     2657     -120     
+ Misses       2831     2783      -48     
+ Partials      305      295      -10     

Impacted Files	Coverage Δ
pkg/document/crdt/rga_tree_split.go	73.50% <ø> (-0.25%)	⬇️
pkg/document/crdt/text.go	59.37% <67.44%> (+10.93%)	⬆️
api/converter/from_bytes.go	64.41% <100.00%> (-0.01%)	⬇️
api/converter/from_pb.go	54.77% <100.00%> (-0.83%)	⬇️
api/converter/to_bytes.go	83.48% <100.00%> (-2.35%)	⬇️
api/converter/to_pb.go	63.90% <100.00%> (-1.93%)	⬇️

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