[PORT]Add sentenceCase && titleCase builtin function

[Danieladu]

Fixes #2285

• Add sentenceCase function
  capitalize first letter of the first word and use lowercase for everything else.
  for example:

 sentenceCase('') -> '' 
 sentenceCase('a')  -> 'A'
 sentenceCase('abc') -> 'Abc'
 sentenceCase('aBC') -> 'Abc'

• Add titleCase funtion
  Capitalize first letter of each word and use lowercase for everything else.
  for example:

 titleCase('') -> '' 
 titleCase('a')  -> 'A'
 titleCase('abc def') -> 'Abc Def'
 titleCase('aBC') -> 'Abc'

[coveralls]

Pull Request Test Coverage Report for Build 134480

• 8 of 10 (80.0%) changed or added relevant lines in 2 files are covered.
• 9 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.08%) to 80.281%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
libraries/adaptive-expressions/src/expressionFunctions.ts	6	8	75.0%

Files with Coverage Reduction	New Missed Lines	%
libraries/botframework-streaming/src/webSocket/webSocketTransport.ts	2	80.65%
libraries/botframework-streaming/src/webSocket/webSocketServer.ts	7	66.67%

Totals
Change from base Build 134023:	-0.08%
Covered Lines:	12700
Relevant Lines:	15103

---

💛 - Coveralls