[http-client-csharp] Skip unnecessary simplifier passes

[live1206]

Summary

Optimize generated C# post-processing by reducing provably safe qualified names before running the full Roslyn simplifier.

The new pass targets qualified names such as global::System.Uri / System.ClientModel.ClientResult and uses Roslyn speculative binding to replace them with the rightmost name only when the replacement binds to the same symbol in the same semantic model. Unsafe or unsupported cases are left for the normal Roslyn simplifier.

This keeps generated output stable while reducing the amount of semantic name-reduction work left for Simplifier.ReduceAsync.

Motivation

While profiling Azure.ResourceManager.Network generation through the Azure management generator, Roslyn post-processing dominated the direct .NET generator run time. The hotspot was semantic name simplification / global-qualified name reduction in the shared MTG GeneratedCodeWorkspace.ProcessDocument path.

The no-simplifier comparison showed that global:: / name simplification was by far the largest category: 98,190 diff blocks across 3,534 files. However, skipping or narrowing the simplifier is not a valid product fix because generated output/functionality can be missed or changed.

Latest Network direct-generator measurement

Validated against the same Network saved tspCodeModel.json / Configuration.json direct-generator path. A fresh no-reducer baseline and reducer run produced identical src/Generated output (diff -qr returned no differences).

Run	Internal total	Shell elapsed	Notes
Fresh broad/member-span baseline without reducer	00:19:47.50	1190.835s	Same saved Network inputs; output exactly matched reducer run.
This PR: targeted qualified-name reducer	00:14:04.68	847.959s	Same saved Network inputs; output exactly matched fresh baseline.
Improvement	~5m43s	~343s	Roughly 29% wall-clock reduction for the direct .NET generator phase.

Phase markers from the reducer run:

Phase marker	Cumulative elapsed
All generated type providers built	00:00:03.94
All visitors applied	00:00:11.44
Generated types written into memory	00:00:17.66
Roslyn post-processing complete	00:14:02.90
All files written to disk	00:14:04.68

Output sanity check after the Network run:

Token	Count	Files
global::System	2	1
this.	31	6
<see cref="global::	0	0

Implementation notes

• The reducer runs after member removal and generator rewriters, then refreshes the syntax root before the existing simplifier step.
• It considers outer QualifiedNameSyntax / AliasQualifiedNameSyntax nodes and skips unsupported contexts such as using directives and XML cref.
• It compares the original symbol to the speculative replacement symbol using SymbolEqualityComparer.Default in the same semantic model.
• It only replaces names that bind equivalently; everything else remains for the normal Roslyn simplifier.
• The existing simplifier still runs over spans containing remaining reducible forms (this., parenthesized expressions, cref, qualified names, member access expressions, assignments, etc.).

Validation

cd packages/http-client-csharp
npm run build:generator
pwsh ./eng/scripts/Generate.ps1
npm run test:generator

Local validation results:

• npm run build:generator passed.
• pwsh ./eng/scripts/Generate.ps1 produced no generated test-project diffs.
• npm run test:generator passed.
• Network direct-generator profiling improved from 00:19:47.50 to 00:14:04.68 internal time on the same saved inputs, with no generated output differences versus the fresh baseline.

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npm i https://pkg.pr.new/@typespec/http-client-csharp@10846

commit: 53124ea

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