Improve grammar and expressions for American English

[Copilot]

This PR addresses grammatical issues and non-idiomatic expressions throughout the Symfony documentation to make it more natural for native American English speakers, as requested in the issue.

Changes Made

Language Inclusivity

• Replaced "master" terminology with more inclusive alternatives like "learn" and "understand"
• Updated "dummy" references to use "test" in technical contexts

Grammar Fixes

• Article usage: Fixed missing articles (e.g., "Easy way" → "An easy way")
• Verb forms: Corrected constructions like "allow to define" → "allow you to define"
• Word order: Fixed awkward ordering like "read first the" → "first read the" and "knowing first" → "first knowing"
• Subject-verb agreement: Fixed "some part...which modify" → "some parts...that modify"
• Prepositions: Improved usage like "know of:" → "know:"

Style Improvements

• Replaced potentially problematic terms flagged by linting tools:
  • "straightforward" → "simple"
  • "just" → more specific alternatives like "only" or removed entirely
  • "more deeply" → "more"
• Improved sentence flow with better conjunctions ("but is" → "but rather")
• Added missing commas for clarity

Files Modified

• page_creation.rst, routing.rst, security.rst, controller.rst
• event_dispatcher.rst, http_cache.rst, mailer.rst, mercure.rst
• messenger.rst, translation.rst, workflow.rst, cache.rst
• configuration.rst, testing.rst, best_practices.rst, bundles.rst
• deployment.rst, lock.rst, serializer.rst

Quality Assurance

• Used Alex linting tool to identify language issues
• Preserved all technical accuracy and meaning
• Focused on high-traffic documentation files
• Remaining linting warnings are mostly false positives for technical terms

These changes make the documentation more accessible and natural-sounding for native English speakers while maintaining the technical precision that developers expect.

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