[LG] treat everything after first '=' as value for the property

[Danieladu]

close: #3339

Originally, if you want to input '=' in the structure value, an escape should be added. like:

# welcome(name)
[Activity
  text = hi, name \= @{name}
]

But now, we just treat the first equals mark as the key/value separator, so, we can write is as:

# welcome(name)
[Activity
  text = hi, name = @{name}
]

there is no need to write the backslash.

[coveralls]

Pull Request Test Coverage Report for Build 103817

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 16 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.001%) to 79.539%

---

Files with Coverage Reduction	New Missed Lines	%
/libraries/Microsoft.Bot.Builder.LanguageGeneration/obj/Release/netstandard2.0/LGFileLexer.cs	16	91.45%

Totals
Change from base Build 103712:	-0.001%
Covered Lines:	10869
Relevant Lines:	13665

---

💛 - Coveralls

[fuselabs]

✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.dll compared against version 4.6.3
✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.AI.Luis.dll compared against version 4.6.3
✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.AI.QnA.dll compared against version 4.6.3
✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.ApplicationInsights.dll compared against version 4.6.3
✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.Azure.dll compared against version 4.6.3
✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.Dialogs.dll compared against version 4.6.3
✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.Integration.ApplicationInsights.Core.dll compared against version 4.6.3
✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.Integration.AspNet.Core.dll compared against version 4.6.3
✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.TemplateManager.dll compared against version 4.6.3
✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.Testing.dll compared against version 4.6.3
✔️ No Binary Compatibility issues for Microsoft.Bot.Configuration.dll compared against version 4.6.3
✔️ No Binary Compatibility issues for Microsoft.Bot.Connector.dll compared against version 4.6.3
✔️ No Binary Compatibility issues for Microsoft.Bot.Schema.dll compared against version 4.6.3
✔️ No Binary Compatibility issues for Microsoft.Bot.Streaming.dll compared against version 4.6.3