docs(contribute): add pitching loaders section to writing-a-loader

[raj-sapalya]

What kind of change does this PR introduce?
Documentation improvement — adds a missing section on pitching loaders.

Summary

The writing-a-loader guide covers simple and complex loader usage
but does not include a section on pitching loaders. The pitch phase is
one of the most confusing topics for loader authors — the left-to-right
execution, the data object, and short-circuiting behavior are not
intuitive without a concrete example.

This PR adds a ## Pitching loaders section with:

• A working example showing data passing from pitch to the normal phase
• A short-circuit example demonstrating early return behavior
• A T> tip clarifying that data is shared only within the same loader
• A W> warning explaining that the normal phase is skipped on short-circuit

Does this PR introduce a breaking change?
No.

What needs to be documented once your changes are merged?
Nothing additional.

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Project	Deployment	Actions	Updated (UTC)
webpack-js-org	Ready	Preview, Comment	Apr 14, 2026 5:13pm