Improve the evaluate requests (#2583)

Currently it evaluates the given expression in the context of the top most stack frame.
The expression should access to any variables and arguments that are in the scope chain.
Implement the eval_at request with the level of the scope chain as a further argument.

JerryScript-DCO-1.0-Signed-off-by: Robert Sipka rsipka.uszeged@partner.samsung.com

tests/debugger/do_eval_at.expected

@@ -0,0 +1,44 @@
+Connecting to: localhost:5001
+Stopped at tests/debugger/do_eval_at.js:15
+(jerry-debugger) eval_at 0
+undefined
+(jerry-debugger) eval_at 0 b
+undefined
+(jerry-debugger) n
+Stopped at tests/debugger/do_eval_at.js:23
+(jerry-debugger) eval_at 0 b
+2
+(jerry-debugger) b do_eval_at.js:20
+Breakpoint 1 at tests/debugger/do_eval_at.js:20 (in f() at line:17, col:1)
+(jerry-debugger) n
+Stopped at breakpoint:1 tests/debugger/do_eval_at.js:20 (in f() at line:17, col:1)
+(jerry-debugger) scopes
+level | type   
+0     | local  
+1     | global 
+(jerry-debugger) eval_at 0 b
+6
+(jerry-debugger) eval_at 1 b
+2
+(jerry-debugger) eval_at 0 b=20
+20
+(jerry-debugger) eval_at 1 b=100
+100
+(jerry-debugger) n
+Stopped at tests/debugger/do_eval_at.js:25
+(jerry-debugger) eval_at 0 a
+23
+(jerry-debugger) scopes
+level | type   
+0     | global 
+(jerry-debugger) eval_at 0 b
+100
+(jerry-debugger) eval_at -1 b
+Error: Invalid scope chain index: -1 (must be between 0 and 65535)
+(jerry-debugger) eval_at 65536 b
+Error: Invalid scope chain index: 65536 (must be between 0 and 65535)
+(jerry-debugger) eval_at b
+Error: invalid literal for int() with base 10: 'b'
+(jerry-debugger) eval_at 200
+Uncaught exception: Error
+(jerry-debugger) c