[SRM] Miscellaneous clean-up.

[teo-tsirpanis]

This PR contains various small changes to System.Reflection.Metadata that have been noticed since some time, some of which being cherry-picked from #115294, to reduce its scope.

[Copilot]

Pull request overview

This PR performs a set of small cleanups in System.Reflection.Metadata, primarily simplifying internal helpers and reducing custom/unsafe code paths.

Changes:

• Simplifies PE header/stub writing and embedded PDB decompression code paths.
• Reduces custom UTF-8 helper usage by switching several call sites to Encoding.UTF8/char APIs.
• Consolidates EncodingHelper implementation and removes unused internal APIs/tests (e.g., Hash.Combine(bool, …) and related test).

Reviewed changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/libraries/System.Reflection.Metadata/tests/Utilities/HashTests.cs	Removes test for deleted Hash.Combine(bool, int) overload.
src/libraries/System.Reflection.Metadata/src/System/Reflection/PortableExecutable/PEReader.EmbeddedPortablePdb.cs	Uses Stream.ReadAtLeast on .NET builds instead of a custom TryReadAll(Span<byte>) helper.
src/libraries/System.Reflection.Metadata/src/System/Reflection/PortableExecutable/PEHeaderBuilder.cs	Computes header size from PEBuilder.DosHeader.Length rather than a separate constant.
src/libraries/System.Reflection.Metadata/src/System/Reflection/PortableExecutable/PEBuilder.cs	Simplifies DOS stub write path and removes DosHeaderSize constant.
src/libraries/System.Reflection.Metadata/src/System/Reflection/Metadata/MetadataReader.cs	Changes GetBlobContent to request non-unique blob bytes.
src/libraries/System.Reflection.Metadata/src/System/Reflection/Metadata/Internal/BlobHeap.cs	Adds unique option to GetBytes and threads it through virtual blob handling.
src/libraries/System.Reflection.Metadata/src/System/Reflection/Metadata/IL/MethodBodyBlock.cs	Uses ImmutableArray builder + MoveToImmutable() for exception region reading.
src/libraries/System.Reflection.Metadata/src/System/Reflection/Metadata/Ecma335/PortablePdbBuilder.cs	Switches UTF-8 byte count assert to Encoding.UTF8.
src/libraries/System.Reflection.Metadata/src/System/Reflection/Metadata/Ecma335/MetadataRootBuilder.cs	Uses Encoding.UTF8.GetByteCount instead of BlobUtilities.GetUTF8ByteCount(string).
src/libraries/System.Reflection.Metadata/src/System/Reflection/Metadata/Ecma335/MetadataBuilder.Heaps.cs	Replaces custom surrogate helpers/UTF-8 byte count with char/Encoding.UTF8 APIs in string heap serialization logic.
src/libraries/System.Reflection.Metadata/src/System/Reflection/Metadata/BlobWriter.cs	Uses Encoding.UTF8.GetByteCount(char*, int) when calculating UTF-8 write size.
src/libraries/System.Reflection.Metadata/src/System/Reflection/Internal/Utilities/StreamExtensions.cs	Removes .NET-only TryReadAll(Span<byte>) overload.
src/libraries/System.Reflection.Metadata/src/System/Reflection/Internal/Utilities/Hash.cs	Removes unused Hash.Combine(bool, int) overload.
src/libraries/System.Reflection.Metadata/src/System/Reflection/Internal/Utilities/EncodingHelper.netcoreapp.cs	Deletes the netcoreapp-specific implementation.
src/libraries/System.Reflection.Metadata/src/System/Reflection/Internal/Utilities/EncodingHelper.cs	Consolidates implementation and switches to ArrayPool<byte>.Shared for prefixed decoding.
src/libraries/System.Reflection.Metadata/src/System/Reflection/Internal/Utilities/BlobUtilities.cs	Replaces custom surrogate helpers with char APIs and removes GetUTF8ByteCount(string) helper.
src/libraries/System.Reflection.Metadata/src/System.Reflection.Metadata.csproj	Consolidates EncodingHelper compile include and removes conditional file inclusion; also normalizes the project file header.

[Copilot]

Pull request overview

Copilot reviewed 18 out of 18 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 21 out of 21 changed files in this pull request and generated no new comments.

[jkotas]

/ba-g Known issue #127341 that has been fixed in main already