[java] Avoid creating a new String to qualify types

[jsotuyod]

• This is now slightly faster, which for a method that gets called
  over 1 million times on large projects is significant.
• We should still look for ways to reduce the number of calls to this
  method.

This alone was enough to shave ~15% from analysis time when running the exact same test as used in #117

The baseline for PMD 5.5.2 was:

--------------------------------<<< Summary >>>--------------------------------
Segment                                         Time (secs)

Collect files:                                        0.241
Load rules:                                           0.053
Parser:                                               6.216
Symbol table:                                        16.711
RuleChain visit:                                      0.290
Reporting:                                            0.055
Rule total:                                           0.000
Rule chain rule total:                                0.000
Rule Average (0 rules):                               0.000
RuleChain Average (4 rules):                          0.216

-----------------------------<<< Final Summary >>>-----------------------------
Total                                           Time (secs)

Measured total:                                      24.432
Non-measured total:                                   0.547
Total PMD:                                           24.979

This single change produces:

--------------------------------<<< Summary >>>--------------------------------
Segment                                         Time (secs)

Collect files:                                        0.285
Load rules:                                           0.054
Parser:                                               6.106
Symbol table:                                        13.346
RuleChain visit:                                      0.275
Reporting:                                            0.051
Rule total:                                           0.000
Rule chain rule total:                                0.000
Rule Average (0 rules):                               0.000
RuleChain Average (4 rules):                          0.224

-----------------------------<<< Final Summary >>>-----------------------------
Total                                           Time (secs)

Measured total:                                      21.014
Non-measured total:                                   0.590
Total PMD:                                           21.603

All numbers are close enough to disregard measuring noise, the only significant difference is for Symbol Table being 3.4 secs faster.

[adangel]

Wow, little change, big effect!
I think, this is small enough to also cherry-pick to 5.4.x and 5.5.x. WDYT?

[jsotuyod]

Sure, it's small enough to be harmless, and the effect is huge, so it would be more than welcome by 5.4.x users.

[adangel]

Thanks! I've merged it into 5.4.x, 5.5.x and master.