Defer semantic3 running of generated `opAssign` function, and add special
error gagging mechanism in `FuncDeclaration.semantic3()` to hide errors
from its body.

Add STCinference for attribute inference of opAssign/postblit/destructor.

[REG2.068.0] Issue 15044 - destroy might leak memory

…stack unwinding"

This reverts commit e20c63c.

# Conflicts:
#	test/runnable/sdtor.d

- Unstored RAII struct return yields bogus error

add test for Issue 15056 - Unstored RAII struct return yields bogus error

Conflicts:
	changelog.dd
	src/opover.c
	src/posix.mak
	test/runnable/sdtor.d

Conflicts:
	src/access.d
	src/aggregate.d
	src/aliasthis.d
	src/apply.d
	src/argtypes.d
	src/arrayop.d
	src/arraytypes.d
	src/attrib.d
	src/builtin.d
	src/canthrow.d
	src/clone.d
	src/cond.d
	src/constfold.d
	src/cppmangle.d
	src/ctfeexpr.d
	src/dcast.d
	src/dclass.d
	src/declaration.d
	src/declaration.h
	src/delegatize.d
	src/denum.d
	src/dimport.d
	src/dinifile.d
	src/dinterpret.d
	src/dmacro.d
	src/dmangle.d
	src/dmodule.d
	src/doc.d
	src/dscope.d
	src/dstruct.d
	src/dsymbol.d
	src/dtemplate.d
	src/dunittest.d
	src/dversion.d
	src/errors.d
	src/escape.d
	src/expression.d
	src/func.d
	src/globals.d
	src/hdrgen.d
	src/identifier.d
	src/init.d
	src/inline.d
	src/json.d
	src/lexer.d
	src/lib.d
	src/link.d
	src/magicport.json
	src/mars.d
	src/mtype.d
	src/nogc.d
	src/nspace.d
	src/objc.d
	src/opover.d
	src/optimize.d
	src/parse.d
	src/root/file.d
	src/root/filename.d
	src/root/man.d
	src/root/outbuffer.d
	src/root/speller.d
	src/sapply.d
	src/sideeffect.d
	src/statement.d
	src/staticassert.d
	src/target.d
	src/tokens.d
	src/traits.d
	src/visitor.d
	test/runnable/sdtor.d

Merge branch 'merge_stable_convert' into merge_stable