code cleanup

[dsyme]

• Split TcAnonRecdExpr into two functions
• ExtensionTyping.fs{i} --> TypeProviders.fs{i} plus remove indentation
• Clarify some cases of confusing single character identifiers such as e --> expr or exn
• Clarify some uses of "tick identifiers", e.g. body' --> bodyR
• Some whitespace cleanup
• Normalize and clarify some commonly occuring identifiers, e.g. rty --> retTy or other as necessary, bodyty --> bodyTy
• Remove some uses of List.iter and Array.iter in favour of explicit for loops, which we generally prefer in the compiler.

Some general rules

• Tick identifiers body' are not that great. They are generally harder to read and can't be inspected in the debugger as things stand. Generaly use R suffix instead, e.g. bodyR. The R can stand for "rewritten" or "result"
• Abbreviations that run together lowercase like bodyty are bad, really hard to head for newcomers
• Don't use List.iter and Array.iter in the compiler, a for loop is simpler

[dsyme]

@vzarytovskii This is ready for review