Explicit Api mode: Renamings after design discussions

Change CLI flag to -Xexplicit-api=strict|warning. 'Disable' state and 'mode' suffix are left out as implementation details.

Change intention title to 'make X public explicitly'

Do not report 'no explicit visibility' on property accessors

Set DECLARATION_SIGNATURE as a range for report

Rename internal diagnostic from _MIGRATION to _WARNING

compiler/testData/cli/js/jsExtraHelp.out

@@ -11,9 +11,6 @@ where advanced options include:
   -Xtyped-arrays             Translate primitive arrays to JS typed arrays
   -Xallow-kotlin-package     Allow compiling code in package 'kotlin' and allow not requiring kotlin.stdlib in module-info
   -Xallow-result-return-type Allow compiling code when `kotlin.Result` is used as a return type
-  -Xapi-mode={enable|disable|migration}
-                             Enable api mode, force compiler to report errors an all public API declarations without explicit visibility.
-                             Use 'migration' level to issue warnings instead of errors.
   -Xcheck-phase-conditions   Check pre- and postconditions on phases
   -Xcheck-sticky-phase-conditions
                              Run sticky condition checks on subsequent phases as well. Implies -Xcheck-phase-conditions
@@ -29,6 +26,9 @@ where advanced options include:
   -Xdump-perf=<path>         Dump detailed performance statistics to the specified file
   -Xeffect-system            Enable experimental language feature: effect system
   -Xexperimental=<fq.name>   Enable and propagate usages of experimental API for marker annotation with the given fully qualified name
+  -Xexplicit-api={strict|warning|disable}
+                             Force compiler to report errors an all public API declarations without explicit visibility.
+                             Use 'warning' level to issue warnings instead of errors.
   -Xinline-classes           Enable experimental inline classes
   -Xintellij-plugin-root=<path> Path to the kotlin-compiler.jar or directory where IntelliJ configuration files can be found
   -Xlegacy-smart-cast-after-try Allow var smart casts despite assignment in try block