Replace TemplateContextType.isInContext deprecated method

[juan-mora-google]

Description

Replaced deprecated method isInContext from TemplateContextType class in DartTemplateContextType.java file

Note: Work of this PR was originally here, but it was closed due to CLA problems.

Testing steps:

1. Run the IDE in Sandbox mode with the plugin
2. Prepare a Live Template for testing
Inside the Sandbox IDE window:

• Go to the IDE settings (Settings / Preferences).
• Navigate to Editor > Live Templates.
• Click the + (Add) button and select Live Template.
• Give it an abbreviation (e.g., dtest) and some template code (e.g., print('hello');).
• At the bottom, you will see a red warning saying "No applicable contexts". Click Define.
• Find Dart option (which matches the contextId registered in the plugin.xml) and check it.
• Apply.

3. Test the "Happy Path" (It should work)

• Create a .dart file inside the Sandbox IDE
• Start typing the abbreviation previously defined (dtest).
• The IDE should suggest the template. If you press Tab, the code will expand. This confirms that file.getLanguage() instanceof DartLanguage evaluated to true.

4. Test the "Negative Path" (It should not work)

• Create a file with a different extension in the same project, for example test.java or test.txt.
• Attempt to type the abbreviation (dtest).
• The IDE should not suggest or expand the template, since the condition requiring it to be a DartLanguage file is not met.

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• I've updated CHANGELOG.md if appropriate (i.e. user-facing change) (N/A)

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[gemini-code-assist]

Code Review

This pull request updates DartTemplateContextType.java to override the newer signature of isInContext that accepts a TemplateActionContext instead of PsiFile and int offset. It extracts the file and start offset from the context object to perform the language and element checks. There are no review comments, so I have no feedback to provide.

[pq]

The testing steps are great. Thanks!