Fixed String(int64_t)

[mrengineer7777]

Description of Change

Fixed int64_t String support.

Background:
sprintf on esp32 doesn't support "%lld" parameter. It's possible to recompile the underlying libraries to add that option. However this has already been solved in ESP8266 version of WString by replacing sprintf() with itoa/ltoa/lltoa.

This PR does the following:
Fixes integer print issues by replacing sprintf() with itoa/ltoa/lltoa
Moves concat(long long num), concat(unsigned long long num) location (match ESP8266)
Cleans up code formatting (matches ESP8266)

Tests scenarios

Tested on Arduino FeatherESP32 with v2.0.5 and current master.

Related links

Closes #7760

[mrengineer7777]

Rebased PR on latest master. Had to undo moved functions, rebase, move again, squash changes and force push.

[mrengineer7777]

I built a test project to verify String integer conversion functionality. https://github.com/mrengineer7777/WStringTEST

Testing against arduino-esp32 v2.0.5:
10:36:31.784 > -------------WString Testing---------------
10:36:31.785 > Constructor Tests
10:36:31.785 > char Expecting a, a, got a, a
10:36:31.785 > int Expecting -12345, 12345, got -12345, 12345
10:36:31.785 > long Expecting -123456, 123456, got -123456, 123456
10:36:31.785 > long Expecting -12345678, 12345678, got ld, 12345678 [FAILED]
10:36:31.785 > Concat Tests
10:36:31.785 > char Expecting a, a, got a, 97 [LEGACY]
10:36:31.785 > int Expecting -12345, 12345, got -12345, 12345
10:36:31.785 > long Expecting -123456, 123456, got -123456, 123456
10:36:31.785 > long long Expecting -12345678, 12345678, got ld, 12345678 [FAILED]
10:36:31.785 > ---Tests completed---

Note the failures on long long.

Testing with proposed PR, including changes to WString from master:
10:48:41.439 > -------------WString Testing---------------
10:48:41.440 > Constructor Tests
10:48:41.440 > char Expecting a, a, got a, a
10:48:41.440 > int Expecting -12345, 12345, got -12345, 12345
10:48:41.440 > long Expecting -123456, 123456, got -123456, 123456
10:48:41.440 > long Expecting -12345678, 12345678, got -12345678, 12345678
10:48:41.440 > Concat Tests
10:48:41.440 > char Expecting a, a, got a, 97 [LEGACY]
10:48:41.440 > int Expecting -12345, 12345, got -12345, 12345
10:48:41.440 > long Expecting -123456, 123456, got -123456, 123456
10:48:41.440 > long long Expecting -12345678, 12345678, got -12345678, 12345678
10:48:41.440 > ---Tests completed---

Note this PR resolves the failure on long long but otherwise does NOT change existing behavior.
Also note that char appears to convert inconsistently (possibly due to cast to int). This PR does not change that.

[mrengineer7777]

@SuGlider Ready for review