gdb/mi: fix breakpoint script field output

gdb/mi: fix breakpoint script field output

The "script" field, output whenever information about a breakpoint with
commands is output, uses wrong MI syntax.

    $ ./gdb -nx -q --data-directory=data-directory -x script -i mi
    =thread-group-added,id="i1"
    =breakpoint-created,bkpt={number="1",type="breakpoint",disp="keep",enabled="y",addr="0x000000000000111d",func="main",file="test.c",fullname="/home/simark/build/binutils-gdb-one-target/gdb/test.c",line="3",thread-groups=["i1"],times="0",original-location="main"}
    =breakpoint-modified,bkpt={number="1",type="breakpoint",disp="keep",enabled="y",addr="0x000000000000111d",func="main",file="test.c",fullname="/home/simark/build/binutils-gdb-one-target/gdb/test.c",line="3",thread-groups=["i1"],times="0",script={"aaa","bbb","ccc"},original-location="main"}
    (gdb)
    -break-info
    ^done,BreakpointTable={nr_rows="1",nr_cols="6",hdr=[{width="7",alignment="-1",col_name="number",colhdr="Num"},{width="14",alignment="-1",col_name="type",colhdr="Type"},{width="4",alignment="-1",col_name="disp",colhdr="Disp"},{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},{width="18",alignment="-1",col_name="addr",colhdr="Address"},{width="40",alignment="2",col_name="what",colhdr="What"}],body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",addr="0x000000000000111d",func="main",file="test.c",fullname="/home/simark/build/binutils-gdb-one-target/gdb/test.c",line="3",thread-groups=["i1"],times="0",script={"aaa","bbb","ccc"},original-location="main"}]}
    (gdb)

In both the =breakpoint-modified and -break-info output, we have:

     script={"aaa","bbb","ccc"}

According to the output syntax [1], curly braces means tuple, and a
tuple contains key=value pairs.  This looks like it should be a list,
but uses curly braces by mistake.  This would make more sense:

    script=["aaa","bbb","ccc"]

Fix it, keeping the backwards compatibility by introducing a new MI
version (MI4), in exactly the same way as was done when fixing
multi-locations breakpoint output in [2].

 - Add a fix_breakpoint_script_output uiout flag.  MI uiouts will use
   this flag if the version is >= 4.
 - Add a fix_breakpoint_script_output_globally variable and the
   -fix-breakpoint-script-output MI command to set it, if frontends want
   to use the fixed output for this without using the newer MI version.
 - When emitting the script field, use list instead of tuple, if we want
   the fixed output (depending on the two criteria above)
 -

[1] https://sourceware.org/gdb/onlinedocs/gdb/GDB_002fMI-Output-Syntax.html#GDB_002fMI-Output-Syntax
[2] https://gitlab.com/gnutools/binutils-gdb/-/commit/b4be1b0648608a2578bbed39841c8ee411773edd

Change-Id: I7113c6892832c8d6805badb06ce42496677e2242
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=24285