Add basic support for conditional breakpoints

This is the minimal required for a user to use conditional breakpoint -
we add an options dict to each breakpoint (line and function) and allow
the condition to be supplied. We add a plug mapping and a default
shortcut (<leader><F9>) to add one where we ask the user to enter the
condition and hit expression. This isn't great but it works.

We don't check the capabilities, so they would just be ignored if used
on a server that doesn't support them. We also ask for a hit expression
which most users won't understand so this isn't ideal either.

No tests yet.

plugin/vimspector.vim

@@ -43,6 +43,11 @@ nnoremap <Plug>VimspectorRestart        :<c-u>call vimspector#Restart()<CR>
 nnoremap <Plug>VimspectorPause          :<c-u>call vimspector#Pause()<CR>
 nnoremap <Plug>VimspectorToggleBreakpoint
       \ :<c-u>call vimspector#ToggleBreakpoint()<CR>
+nnoremap <Plug>VimspectorToggleConditionalBreakpoint
+      \ :<c-u>call vimspector#ToggleBreakpoint(
+                    \ { 'condition': input( 'Enter condition: ' ),
+                    \   'hitCondition': input( 'Enter hit condition: ' ) }
+                    \ )<CR>
 nnoremap <Plug>VimspectorAddFunctionBreakpoint
       \ :<c-u>call vimspector#AddFunctionBreakpoint( expand( '<cexpr>' ) )<CR>
 nnoremap <Plug>VimspectorStepOver       :<c-u>call vimspector#StepOver()<CR>
@@ -65,6 +70,7 @@ elseif s:mappings ==# 'HUMAN'
   nmap <F4>         <Plug>VimspectorRestart
   nmap <F6>         <Plug>VimspectorPause
   nmap <F9>         <Plug>VimspectorToggleBreakpoint
+  nmap <leader><F9> <Plug>VimspectorToggleConditionalBreakpoint
   nmap <F8>         <Plug>VimspectorAddFunctionBreakpoint
   nmap <F10>        <Plug>VimspectorStepOver
   nmap <F11>        <Plug>VimspectorStepInto