even lighter version of #17938: fix most issues with UnusedImport, XDeclaredButNotUsed, etc; fix #17511, #17510, #14246 (without realModule) (#18362)

* {.used: symbol}

* add tests

* fix tests with --import

* --import works without giving spurious unused warnings

* new warning warnDuplicateModuleImport for `import foo; import foo`

* fix test, add resolveModuleAlias, use proper line info for module aliases

* fix spurious warnings

* fix deprecation msg for deprecated modules even with `import foo as bar`

* disable a test for i386 pending sorting XDeclaredButNotUsed errors

* UnusedImport now works with re-exported symbols

* fix typo [skip ci]

* ic support

* add genPNode to allow writing PNode-based compiler code similarly to `genAst`

* fix DuplicateModuleImport warning

* adjust test

* fixup

* fixup

* fixup

* fix after rebase

* fix for IC

* keep the proc inline, move the const out

* [skip ci] fix changelog

* experiment: remove calls to resolveModuleAlias

* followup

* fixup

* fix tests/modules/tselfimport.nim

* workaround tests/deprecated/tmodule1.nim

* fix properly

* simplify

testament/categories.nim

@@ -508,6 +508,7 @@ proc icTests(r: var TResults; testsDir: string, cat: Category, options: string;
 
   const tempExt = "_temp.nim"
   for it in walkDirRec(testsDir):
+  # for it in ["tests/ic/timports.nim"]: # debugging: to try a specific test
     if isTestFile(it) and not it.endsWith(tempExt):
       let nimcache = nimcacheDir(it, options, getTestSpecTarget())
       removeDir(nimcache)