fix(mac): turn on legacy mode for Java apps

Relates to #3935.

This switches Java apps into legacy mode. However, Java itself will need
patching to support Keyman, as it makes assumptions about input methods,
including matching specific input methods by name, before enabling its
complex text support.

I am in process of submitting a bug report and may try and submit a
patch (although the process seems a little convoluted). It requires a
change to a single file, AWTView.m, with the following diff (against
JDK 16.0):

diff --git a/src/java.desktop/macosx/native/libawt_lwawt/awt/AWTView.m b/src/java.desktop/macosx/native/libawt_lwawt/awt/AWTView.m
index 3e80b5a6cf3..2ae1f4f3f12 100644
--- a/src/java.desktop/macosx/native/libawt_lwawt/awt/AWTView.m
+++ b/src/java.desktop/macosx/native/libawt_lwawt/awt/AWTView.m
@@ -263,6 +263,16 @@ - (void) keyDown: (NSEvent *)event {
     fProcessingKeystroke = YES;
     fKeyEventsNeeded = YES;

+    if([(NSString *)kbdLayout containsString:@"keyman"]) {
+        // Keyman handles all key events; none should be
+        // passed through as default before Keyman processes them
+        fKeyEventsNeeded = NO;
+    }
     // Allow TSM to look at the event and potentially send back NSTextInputClient messages.
     [self interpretKeyEvents:[NSArray arrayWithObject:event]];

@@ -960,7 +989,9 @@ - (void) insertText:(id)aString replacementRange:(NSRange)replacementRange

     if ((utf16Length > 2) ||
         ((utf8Length > 1) && [self isCodePointInUnicodeBlockNeedingIMEvent:codePoint]) ||
-        ((codePoint == 0x5c) && ([(NSString *)kbdLayout containsString:@"Kotoeri"]))) {
+        ((codePoint == 0x5c) && ([(NSString *)kbdLayout containsString:@"Kotoeri"])) ||
+        ([(NSString *)kbdLayout containsString:@"keyman"])
+        ) {
         aStringIsComplex = YES;
     }