[hxb] detect need for local context in nested anons

[kLabz]

Should fix #11589 (the hashlink debugger part)

Leaving as a draft for now, will come back to it on monday tuesday:

• Add a nice compiler message for hxb reader issues to ask user to submit an issue with a bit more context (current module, current chunk, backtrace)
• Add tests for this and the previous fix for Haxe error Invalid_argument("index out of bounds") on JS project compile with --connect #11589
• Make that nested field test pass...
• Properly test this change with Rudy CI ™️

[Simn]

Hmm... I don't fully understand why this is necessary, but it looks cleaner anyway.

[kLabz]

Rudy CI is fine with this (and was broken before), only remaining issues are not related:

• something wrong with unbound type parameters (not sure those should be unbound + compilation breaks afterwards)
• dune isn't compiling with nightlies (locally at least), need to investigate