Improve variable live range JitDump output

[BruceForstall]

The live variable output is unnecessarily verbose. Simplify it; clean it up;
make it smaller; use standard dumpers.

Example, before:

////////////////////////////////////////
////////////////////////////////////////
Variable Live Range History Dump for Block 2
IL Var Num 0:
[rcx [ (G_M13669_IG02,ins#0,ofs#0), (G_M13669_IG03,ins#1,ofs#2) ]; rbp[16] (1 slot) [ (G_M13669_IG03,ins#1,ofs#2), NON_CLOSED_RANGE ]; ]
IL Var Num 1:
[rsi [ (G_M13669_IG03,ins#1,ofs#2), NON_CLOSED_RANGE ]; ]
////////////////////////////////////////
////////////////////////////////////////
End Generating code for Block 2

After:

Variable Live Range History Dump for BB02
V00 this: rcx [(G_M13669_IG02,ins#0,ofs#0), (G_M13669_IG03,ins#1,ofs#2)]; rbp[16] (1 slot) [(G_M13669_IG03,ins#1,ofs#2), ...]
V01 loc0: rsi [(G_M13669_IG03,ins#1,ofs#2), ...]

And the end-of-dump output, before:

////////////////////////////////////////
////////////////////////////////////////
PRINTING VARIABLE LIVE RANGES:
IL Var Num 0:
[rsi [18 , B5 )rsi [100 , 13A )rsi [14D , 186 )rsi [196 , 1C5 )rsi [1E3 , 271 )rsi [280 , 285 )]
IL Var Num 1:
[rdi [18 , B9 )rdi [100 , 137 )rdi [14D , 184 )rdi [196 , 1C2 )rdi [1E3 , 271 )rdi [280 , 288 )]
IL Var Num 2:
[rbx [18 , CA )rbx [100 , 10D )rbx [14D , 15A )rbx [196 , 1C7 )rbx [1E3 , 271 )rbx [280 , 28B )]
IL Var Num 3:
[rbp [3A , F0 )rbp [100 , 141 )rbp [14D , 18C )rbp [196 , 1D6 )rbp [1E3 , 275 )]
IL Var Num 4:
[r14 [3E , EC )r14 [100 , 13D )r14 [14D , 188 )r14 [196 , 1D2 )r14 [1E3 , 271 )]
IL Var Num 5:
[rcx [22A , 263 )]
////////////////////////////////////////
////////////////////////////////////////

After:

VARIABLE LIVE RANGES:
V00 arg0: rsi [18, B5); rsi [100, 13A); rsi [14D, 186); rsi [196, 1C5); rsi [1E3, 271); rsi [280, 285)
V01 arg1: rdi [18, B9); rdi [100, 137); rdi [14D, 184); rdi [196, 1C2); rdi [1E3, 271); rdi [280, 288)
V02 arg2: rbx [18, CA); rbx [100, 10D); rbx [14D, 15A); rbx [196, 1C7); rbx [1E3, 271); rbx [280, 28B)
V03 loc0: rbp [3A, F0); rbp [100, 141); rbp [14D, 18C); rbp [196, 1D6); rbp [1E3, 275)
V04 loc1: r14 [3E, EC); r14 [100, 13D); r14 [14D, 188); r14 [196, 1D2); r14 [1E3, 271)
V05 loc2: rcx [22A, 263)

[BruceForstall]

@dotnet/jit-contrib PTAL

[kunalspathak]

LGTM