Rename clientCtx.JSONMarshaler to JSONCodec

[amaury1093]

Description

follow-up: #9226
ref: #9218
ref: #9226 (comment)

---

Before we can merge this PR, please make sure that all the following items have been
checked off. If any of the checklist items are not applicable, please leave them but
write a little note why.

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the module structure standards.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer
• Review Codecov Report in the comment section below once CI passes

[colin-axner]

utACK

[codecov]

Codecov Report

Merging #9251 (a8fca99) into master (d3bcc15) will not change coverage.
The diff coverage is 87.36%.

@@           Coverage Diff           @@
##           master    #9251   +/-   ##
=======================================
  Coverage   60.14%   60.14%           
=======================================
  Files         595      595           
  Lines       37194    37194           
=======================================
  Hits        22369    22369           
  Misses      12846    12846           
  Partials     1979     1979           

Impacted Files	Coverage Δ
client/keys/add.go	62.50% <0.00%> (ø)
codec/amino_codec.go	100.00% <ø> (ø)
codec/proto_codec.go	73.41% <ø> (ø)
x/distribution/client/cli/tx.go	3.58% <0.00%> (ø)
x/genutil/client/cli/collect.go	0.00% <0.00%> (ø)
x/genutil/client/cli/gentx.go	0.00% <0.00%> (ø)
x/genutil/client/cli/validate_genesis.go	0.00% <0.00%> (ø)
x/genutil/client/testutil/helpers.go	0.00% <0.00%> (ø)
x/gov/client/cli/query.go	0.00% <0.00%> (ø)
x/gov/client/utils/query.go	28.16% <0.00%> (ø)
... and 18 more