Make ApplicationContext inaccessible in ITemplateContext

[JohnNiang]

What type of PR is this?

/kind improvement
/area core
/area plugin
/milestone 2.20.x

What this PR does / why we need it:

This PR disables access to ApplicationContext using ITemplateContext.

Does this PR introduce a user-facing change?

None

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 28 lines in your changes missing coverage. Please review.

Project coverage is 58.04%. Comparing base (6cd8dc8) to head (849335e).
Report is 79 commits behind head on main.

Files with missing lines	Patch %	Lines
.../halo/app/theme/dialect/SecureTemplateContext.java	24.32%	25 Missing and 3 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6680      +/-   ##
============================================
- Coverage     58.18%   58.04%   -0.14%     
- Complexity     3774     3942     +168     
============================================
  Files           651      676      +25     
  Lines         22125    23154    +1029     
  Branches       1538     1579      +41     
============================================
+ Hits          12873    13440     +567     
- Misses         8641     9090     +449     
- Partials        611      624      +13     

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[guqing]

/lgtm

[f2c-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: guqing

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[guqing]

/kind api-change
此 PR 禁止插件通过 SpringContextUtils 获取 ApplicationContext，如果插件使用到此方法则需要使用依赖注入来代替