moderate system cleanup & refactor (#20355)

* system refactor, move out 600 lines

* compilation, slice, backwardsindex, misc_num moved out of system
* some procs/types moved into arithmetics, basic_types
* system no longer depends on syncio
* some procs moved around to fit with their surroundings

* make exceptions an import, old ops to misc_num

* move instantiationInfo back

* move back nim version, fix windows echo

* include compilation

* better docs for imported modules, fix unsigned ops

also remove ze, ze64, toU8, toU16, toU32 with nimPreviewSlimSystem

* fix terminal

* workaround IC test & weird csize bug, changelog

* move NimMajor etc back to compilation, rebase for CI

* try ic fix

* form single `indices`, slim out TaintedString, try fix IC

* fix CI, update changelog, addQuitProc

* fix CI

* try fix CI

* actually fix CI finally hopefully

* Update lib/system/compilation.nim

Co-authored-by: ringabout <43030857+ringabout@users.noreply.github.com>

* update kochdocs

* hopefully fix csize uses for slimsystem

* fix tquit

Co-authored-by: ringabout <43030857+ringabout@users.noreply.github.com>

lib/std/syncio.nim

@@ -39,6 +39,13 @@ type
   FileHandle* = cint ## type that represents an OS file handle; this is
                       ## useful for low-level file access
 
+  FileSeekPos* = enum ## Position relative to which seek should happen.
+                      # The values are ordered so that they match with stdio
+                      # SEEK_SET, SEEK_CUR and SEEK_END respectively.
+    fspSet            ## Seek to absolute value
+    fspCur            ## Seek relative to current position
+    fspEnd            ## Seek relative to end
+
 # text file handling:
 when not defined(nimscript) and not defined(js):
   # duplicated between io and ansi_c
@@ -142,13 +149,6 @@ proc c_fprintf(f: File, frmt: cstring): cint {.
 proc c_fputc(c: char, f: File): cint {.
   importc: "fputc", header: "<stdio.h>".}
 
-# When running nim in android app, stdout goes nowhere, so echo gets ignored
-# To redirect echo to the android logcat, use -d:androidNDK
-when defined(androidNDK):
-  const ANDROID_LOG_VERBOSE = 2.cint
-  proc android_log_print(prio: cint, tag: cstring, fmt: cstring): cint
-    {.importc: "__android_log_print", header: "<android/log.h>", varargs, discardable.}
-
 template sysFatal(exc, msg) =
   raise newException(exc, msg)
 
@@ -791,52 +791,6 @@ proc setStdIoUnbuffered*() {.tags: [], benign.} =
   when declared(stdin):
     discard c_setvbuf(stdin, nil, IONBF, 0)
 
-when declared(stdout):
-  when defined(windows) and compileOption("threads"):
-    proc addSysExitProc(quitProc: proc() {.noconv.}) {.importc: "atexit", header: "<stdlib.h>".}
-
-    const insideRLocksModule = false
-    include "system/syslocks"
-
-
-    var echoLock: SysLock
-    initSysLock echoLock
-    addSysExitProc(proc() {.noconv.} = deinitSys(echoLock))
-
-  const stdOutLock = not defined(windows) and
-                     not defined(android) and
-                     not defined(nintendoswitch) and
-                     not defined(freertos) and
-                     not defined(zephyr) and
-                     hostOS != "any"
-
-  proc echoBinSafe(args: openArray[string]) {.compilerproc.} =
-    when defined(androidNDK):
-      var s = ""
-      for arg in args:
-        s.add arg
-      android_log_print(ANDROID_LOG_VERBOSE, "nim", s)
-    else:
-      # flockfile deadlocks some versions of Android 5.x.x
-      when stdOutLock:
-        proc flockfile(f: File) {.importc, nodecl.}
-        proc funlockfile(f: File) {.importc, nodecl.}
-        flockfile(stdout)
-      when defined(windows) and compileOption("threads"):
-        acquireSys echoLock
-      for s in args:
-        when defined(windows):
-          writeWindows(stdout, s)
-        else:
-          discard c_fwrite(s.cstring, cast[csize_t](s.len), 1, stdout)
-      const linefeed = "\n"
-      discard c_fwrite(linefeed.cstring, linefeed.len, 1, stdout)
-      discard c_fflush(stdout)
-      when stdOutLock:
-        funlockfile(stdout)
-      when defined(windows) and compileOption("threads"):
-        releaseSys echoLock
-
 
 when defined(windows) and not defined(nimscript) and not defined(js):
   # work-around C's sucking abstraction:
@@ -960,3 +914,7 @@ iterator lines*(f: File): string {.tags: [ReadIOEffect].} =
         result.lines += 1
   var res = newStringOfCap(80)
   while f.readLine(res): yield res
+
+template `&=`*(f: File, x: typed) =
+  ## An alias for `write`.
+  write(f, x)