expression: replace `mock.Context` with `StaticExprContext` in tests

[lcwangchao]

What problem does this PR solve?

Issue Number: close #53006

Problem Summary:

After we introduced some static implements for EvalContext and ExprContext. It's better to replace mock.Context with StaticExprContext for the following reasons:

• reduce the dependencies of expression
• make the test easier to maintain without relying on a hug context

What changed and how does it work?

• mock.NewContext is replaced with mockStmtExprCtx
• createContext is replaced with mockStmtTruncateAsWarningExprCtx

Check List

Tests

• [x] Unit test
• [ ] Integration test
• [ ] Manual test (add detailed scripts or steps below)
• [ ] No need to test

  • [ ] I checked and no code files have been changed.

Side effects

• [ ] Performance regression: Consumes more CPU
• [ ] Performance regression: Consumes more Memory
• [ ] Breaking backward compatibility

Documentation

• [ ] Affects user behaviors
• [ ] Contains syntax changes
• [ ] Contains variable changes
• [ ] Contains experimental features
• [ ] Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

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[codecov[bot]]

Codecov Report

Attention: Patch coverage is 80.00000% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 74.5399%. Comparing base (4fe70da) to head (aea6a28). Report is 38 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #53007 +/- ## ================================================ + Coverage 72.4796% 74.5399% +2.0603% ================================================ Files 1493 1493 Lines 429362 429402 +40 ================================================ + Hits 311200 320076 +8876 + Misses 98931 89419 -9512 - Partials 19231 19907 +676 ``` | [Flag](https://app.codecov.io/gh/pingcap/tidb/pull/53007/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pingcap) | Coverage Δ | | |---|---|---| | [integration](https://app.codecov.io/gh/pingcap/tidb/pull/53007/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pingcap) | `49.2460% <40.0000%> (?)` | | | [unit](https://app.codecov.io/gh/pingcap/tidb/pull/53007/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pingcap) | `71.2597% <80.0000%> (-0.1192%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pingcap#carryforward-flags-in-the-pull-request-comment) to find out more. | [Components](https://app.codecov.io/gh/pingcap/tidb/pull/53007/components?src=pr&el=components&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pingcap) | Coverage Δ | | |---|---|---| | [dumpling](https://app.codecov.io/gh/pingcap/tidb/pull/53007/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pingcap) | `53.9957% <ø> (ø)` | | | [parser](https://app.codecov.io/gh/pingcap/tidb/pull/53007/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pingcap) | `∅ <ø> (∅)` | | | [br](https://app.codecov.io/gh/pingcap/tidb/pull/53007/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pingcap) | `50.4684% <ø> (+9.0282%)` | :arrow_up: |

[lcwangchao]

/retest

[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: YangKeao Once this PR has been reviewed and has the lgtm label, please assign xuhuaiyu for approval. For more information see the Code Review Process.

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/pingcap/tidb/blob/master/OWNERS)~~ [YangKeao] - **[pkg/expression/OWNERS](https://github.com/pingcap/tidb/blob/master/pkg/expression/OWNERS)** Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[ti-chi-bot[bot]]

[LGTM Timeline notifier]

Timeline:

• 2024-05-17 05:35:39.678529107 +0000 UTC m=+1804293.435664850: :ballot_box_with_check: agreed by YangKeao.