This adds support for multiple isolates sharing the same module but
setting different breakpoints. This is simulated by having a debugger
test that runs in the "--isolates" variant, i.e. two isolates running
the same test at the same time. Both isolates will set and remove
breakpoints.

The DebugInfo will keep a separate list of breakpoints per isolate, and
when recompiling a function for debugging it will respect all
breakpoints in all isolates.
In order to ensure consistency if multiple isolates are setting or
removing breakpoints simultaneously, we go back to a more coarse-grained
locking scheme, where the DebugInfo lock is held while re-compiling
Liftoff functions.

While recompilation will install the code in the module-global code
table and jump table (and hence all isolates will use it for future
calls), only the stack of the requesting isolate is rewritten to
immediately use new code. This is OK, because other isolates are not
interested in the new breakpoint(s) anyway.
On {SetBreakpoint}, we always need to rewrite the stack of the
requesting isolate though, even if the breakpoint was set before by
another isolate.

Drive-by: Some fixes in SharedFunctionInfo in order to support setting
breakpoints via the Debug mirror.

R=thibaudm@chromium.org

Bug: v8:10359
Change-Id: If659afb273260fc5e8124b4b617fb4322de473c7
Cq-Include-Trybots: luci.v8.try:v8_linux64_tsan_rel
Cq-Include-Trybots: luci.v8.try:v8_linux64_tsan_isolates_rel_ng
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2218059Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68096}