Bug 1796044 - part 16: Make `intl.tsf.enable` a static pref and rename it r=m_kato

Some users may keep disabling TSF while we were improving TSF implementation due
to avoiding some bugs.

Currently, we don't test IMM handler.  Therefore, I think that we should rename
the pref and make users run well-tested path to handle IME.

Depends on D159818

Differential Revision: https://phabricator.services.mozilla.com/D159819

modules/libpref/init/StaticPrefList.yaml

@@ -6868,6 +6868,18 @@
   mirror: always
 
 #ifdef XP_WIN
+  # Whether making Gecko TSF-aware or only working with IMM.  TSF is a modern
+  # IME API set of Windows which replaces IMM APIs.  Unless you can avoid the
+  # problem which you see with enabling TSF, you shouldn't change this pref
+  # to false since IMM handler is now not maintained nor tested with latest
+  # Windows.  If you need to change this pref to false, please file a bug to
+  # <https://bugzilla.mozilla.org>.
+  # Restart required to apply this pref change.
+-   name: intl.tsf.enabled
+    type: bool
+    value: true
+    mirror: once
+
   # Whether Gecko creates or does not create native caret for legacy ATOK
   # (2011 - 2015).
 -   name: intl.tsf.hack.atok.create_native_caret

modules/libpref/init/all.js

@@ -2538,9 +2538,6 @@ pref("font.size.monospace.x-math", 13);
   // Switch the keyboard layout per window
   pref("intl.keyboard.per_window_layout", false);
 
-  // Enable/Disable TSF support.
-  pref("intl.tsf.enable", true);
-
   // If composition_font is set, Gecko sets the font to IME.  IME may use
   // the fonts on their window like candidate window.  If they are empty,
   // Gecko uses the system default font which is set to the IM context.

widget/windows/TSFTextStore.cpp

@@ -51,8 +51,6 @@ static const GUID sGUID_PROP_URL = {
 namespace mozilla {
 namespace widget {
 
-static const char* kPrefNameEnableTSF = "intl.tsf.enable";
-
 /**
  * TSF related code should log its behavior even on release build especially
  * in the interface methods.
@@ -6764,7 +6762,7 @@ void TSFTextStore::Initialize() {
     return;
   }
 
-  bool enableTsf = Preferences::GetBool(kPrefNameEnableTSF, false);
+  const bool enableTsf = StaticPrefs::intl_tsf_enabled_AtStartup();
   MOZ_LOG(gIMELog, LogLevel::Info,
           ("  TSFTextStore::Initialize(), TSF is %s",
            enableTsf ? "enabled" : "disabled"));