Fix typos and improve clarity in documentation

[sami-daniel]

This pull request makes minor documentation improvements across several files to correct spelling, grammar, and phrasing for clarity and consistency. No functional or structural changes are introduced.

Documentation corrections and clarifications:

• Fixed casing and phrasing in the description for warning CS8981 in Warnversion Warning Waves.md to use "lowercase ASCII characters" instead of "lower-cased ascii characters".
• Improved grammar and clarity in sentences describing feature pull decisions and branch differences in Developing a Language Feature.md. [1] [2]
• Corrected punctuation and capitalization in tuple feature documentation, including examples and explanatory text in tuples.md. [1] [2]
• Fixed spelling and phrasing in build error diagnostic instructions, including correcting "being ran" to "being run" and "occured" to "occurred" in Diagnosing-Project-System-Build-Errors.md. [1] [2]

[333fred]

Thanks @sami-daniel!