Normalize whitespace in .csproj files

[xtqqczze]

Ensure all .csproj files have normalized whitespace.

Changes

• Remove trailing whitespace (via regex [ \t]+$).
• Ensure all files end with exactly one newline.
• Ensure encoding is UTF-8 with no byte-order mark

Motivation

The repository's .editorconfig specifies:

trim_trailing_whitespace = true
insert_final_newline = true
charset = utf-8

Many editors enforce these settings automatically. Without normalizing the existing .csproj files, unrelated whitespace changes can show up in otherwise unrelated PRs.

By cleaning this up now, we reduce noise and friction in future contributions.

Notes

• Only whitespace was modified.
• No resource content or functional changes were made.
• A Python script was used to apply the newline changes.
• Excluded src/tests.

Review with whitespace changes hidden

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[stephentoub]

Thank you for your interest in contributing this. However, reviewing more than a thousand files, and incurring change history for more than a thousand files, just for normalization of whitespace, is not something we're going to entertain right now.

[xtqqczze]

d59c66b: Avoid reformatting the runtime tests as they almost never updated. This significantly reduces the volume of changes.