docs: add debugging page describing various flags / strategies to help debugging compiler or a program

[timotheecour]

lots of debugging tools can help understand and debugging the compiler or other programs:

stacktraces

• --stacktrace
• --stackTraceMsgs
• -d:nimCompilerStacktraceHints

misc

• -d:debug

print data structures

• astalgo.debug

instrument compiler

• -d:nimDebugUtils

tracing

• -d:nimVMDebug: trace VM code (very verbose, requires recompiling nim)
• vmutils.vmTrace: trace VM code (doesn't require recompiling nim, can be switched on/off in user code being traced)
• --exectrace: trace regular code, pending https://github.com/nim-lang/Nim/pull/15827 (works but still draft)

links

• analog to https://github.com/timotheecour/Nim/issues/752

[juancarlospaco]

repr for stuff without $

--experimental:strictFuncs can help to find unwanted mutations.

-d:stressOrc ?.

-d:danger for JavaScript targets, because in debug mode, it contains too much noise for run-time checking.

{.exportc.} to skip name manglings of symbols, for debug only.

Styled debug messages to paint bugs red

jsAssert for JS-native assert

Debugger to set debug breakpoints

Temporarily mark symbols with {.deprecated.} to see where is used on the code base.

--expandArc

--expandMacro

not nil may help with read-from-nil bugs.

{.explain.}

Using stricter types, at least temporarily.