new: nim -e:cmd to run a command directly; also fixes #15731 (#15687)

* new: `nim -i cmd`
* rename -i to -e (for eval); consistent with majority of other programing languages
* `nim e -e:cmd` now works; bugfix: `echo cmd | nim e -` now works
* honor --betterRun
* address comments
* --eval alias for -e (replaces undocumented --eval which was a noop)
* --eval now defaults to e (nimscript) instead of r
* address comment: remove -e, only keep --eval
* address comment
* fixup
* Update compiler/nimconf.nim

Co-authored-by: Andreas Rumpf <rumpf_a@web.de>

compiler/options.nim

@@ -246,11 +246,13 @@ type
     evalMacroCounter*: int
     exitcode*: int8
     cmd*: TCommands  # the command
+    cmdInput*: string  # input command
+    projectIsCmd*: bool # whether we're compiling from a command input
+    implicitCmd*: bool # whether some flag triggered an implicit `command`
     selectedGC*: TGCMode       # the selected GC (+)
     exc*: ExceptionSystem
     verbosity*: int            # how verbose the compiler is
     numberOfProcessors*: int   # number of processors
-    evalExpr*: string          # expression for idetools --eval
     lastCmdTime*: float        # when caas is enabled, we measure each command
     symbolFiles*: SymbolFilesOption
 
@@ -418,7 +420,6 @@ proc newConfigRef*(): ConfigRef =
     macrosToExpand: newStringTable(modeStyleInsensitive),
     arcToExpand: newStringTable(modeStyleInsensitive),
     m: initMsgConfig(),
-    evalExpr: "",
     cppDefines: initHashSet[string](),
     headerFile: "", features: {}, legacyFeatures: {}, foreignPackageNotes: {hintProcessing, warnUnknownMagic,
     hintQuitCalled, hintExecuting},