Add WasmFileKeyGenerator for split Wasm symbol files

[paolosevMSFT]

Adds support for indexing WebAssembly modules on symbol servers by introducing a WasmFileKeyGenerator that parses Wasm binaries and extracts the build_id custom section.

This enables uploading and retrieving both halves of split-debug Wasm files. (It follows the same convention as ELF (elf-buildid vs elf-buildid-sym):

• Stripped Wasm modules => indexed with wasm-buildid prefix
• Symbol files (containing DWARF .debug_* sections) => indexed with wasm-buildid-sym prefix

Changes:

• New: WasmFileKeyGenerator class that validates the Wasm header, scans custom sections for build_id, and detects symbol files via .debug_* sections
• Modified: FileKeyGenerator to include WasmFileKeyGenerator in the auto-detection chain
• Tests: Added unit tests with synthetic Wasm binaries covering plain modules, symbol files, and files without build IDs

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[Copilot]

Pull request overview

Adds WebAssembly module support to Microsoft.SymbolStore key generation by introducing a WasmFileKeyGenerator that extracts a build_id custom section and distinguishes stripped vs split-debug Wasm files via .debug_* custom sections, enabling symbol-server indexing using wasm-buildid and wasm-buildid-sym prefixes.

Changes:

• Added WasmFileKeyGenerator to parse Wasm headers/sections, extract build_id, and detect DWARF debug sections.
• Updated FileKeyGenerator auto-detection chain to include Wasm support.
• Added unit tests covering Wasm modules, symbol files, and missing build IDs.

Reviewed changes

Copilot reviewed 3 out of 6 changed files in this pull request and generated 3 comments.

File	Description
src/tests/Microsoft.SymbolStore.UnitTests/KeyGeneratorTests.cs	Adds unit tests for Wasm key generation (module vs symbol file vs missing build_id).
src/Microsoft.SymbolStore/KeyGenerators/WasmFileKeyGenerator.cs	Introduces the Wasm key generator and parsing logic for build_id and .debug_* sections.
src/Microsoft.SymbolStore/KeyGenerators/FileKeyGenerator.cs	Adds Wasm detection to the generic file key generator chain.

Comments suppressed due to low confidence (1)

src/Microsoft.SymbolStore/KeyGenerators/WasmFileKeyGenerator.cs:184

• nameStart is assigned but never used here as well; with TreatWarningsAsErrors enabled this breaks the build. Remove the unused local variable.

                    if (sectionId == CustomSectionId)
                    {
                        long nameStart = stream.Position;
                        string name = ReadWasmString(stream);

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