context: uniform the import naming of context, part 1 (#1773)

[ti-chi-bot]

This is an automated cherry-pick of #1773

What problem does this PR solve?

all context of std lib should be named as context
all context of cdc package should be named as cdcContext

this pr modified the code in ticdc/cdc/processor/pipeline package.

Check List

Tests

• Unit test

Release note

• No release note

[ti-chi-bot]

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[ti-chi-bot]

@ti-chi-bot: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

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[purelind]

/run-unit-tests

[purelind]

/run-leak-tests

[ti-chi-bot]

@ti-chi-bot: PR needs rebase.

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[zier-one]

merged by #2081