Upgrade SiteMesh to 3.3.0-M3

[codeconsole]

Bumps spring-boot-starter-sitemesh / spring-webmvc-sitemesh from 3.3.0-M2 to 3.3.0-M3.

Why

M3 fixes the response charset in the view-resolver integration. Under M2, SiteMeshView stamped a charset-less text/html onto the real response before the inner view rendered. Grails GSP only applies its configured content type (text/html;charset=UTF-8) when none is set yet, so it backed off — and the response went out with the servlet container's locale-derived charset instead. Net effect: decorated pages served most non-English locales as ISO-8859-1, destroying all non-Latin-1 text (Cyrillic, Thai, Chinese, Czech, ...). Only locales whose container mapping happened to be UTF-8 rendered correctly.

M3 lets the inner view own the content type (enableBuffering is now the public API for unconditional buffering) and restores the text/html default only when the view declines to set one.

Also in M3

• The invasive wrap-all default is replaced by a non-invasive delegating resolver — no ViewResolver bean is replaced or retyped. Grails' bean-definition / bean-instance integrations are unaffected and keep priority through the starter's extension contract (verified: single decoration pass).
• SiteMeshViewResolver.decorate(View) for views a handler resolves manually and returns directly.
• SiteMeshViewContext is created after the render, so custom content processors and decorator selectors observe the actual response content type.
• The starter's early post-processors bind sitemesh.* from the Environment, so wrapMode=bean-definition no longer ignores a configured targetBeanName.
• Decorator-chain parsing is centralized and whitespace-tolerant ("inner, outer" works in meta tags, request attributes, and configuration alike).

Verification (against the released Central artifact)

• :grails-sitemesh3:test — green (forced rerun)
• :grails-test-examples-gsp-sitemesh3:check — 21 integration tests green (forced rerun), covering forced layouts, decorator chaining, JSP, plain text, and error-page decoration
• A generated application serves all 18 bundled locales as charset=UTF-8 with strict byte-level validation of the translated content

Companion to #15974, which internationalizes the default welcome page — correct rendering of its non-Latin-1 locales depends on this upgrade.

[jdaugherty]

This is required for us to reroll the 8.0.0-M3 release. I've tested the apps locally and tests and see no issues. I'm merging so we can get teh release out.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 49.6698%. Comparing base (08bd0bf) to head (1c00628).
⚠️ Report is 2 commits behind head on 8.0.x.

Additional details and impacted files

@@                Coverage Diff                 @@
##                8.0.x     #15975        +/-   ##
==================================================
- Coverage     49.6709%   49.6698%   -0.0011%     
  Complexity      17017      17017                
==================================================
  Files            2004       2004                
  Lines           93896      93896                
  Branches        16448      16448                
==================================================
- Hits            46639      46638         -1     
- Misses          40078      40079         +1     
  Partials         7179       7179                

see 1 file with indirect coverage changes

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