Form Recognizer: Rename GetModelInfos() to GetCustomModels()

[annelo-msft]

Was: Form Recognizer: Update naming for ModelInfo/AccountProperties

Decision was only to rename GetModelInfos to GetCustomModels, as shown in: #11792

[annelo-msft]

@samvaity , @kristapratico , did we decide to keep these names the way they are?

[kristapratico]

My understanding was that we'd keep GetAccountProperties the way it is and change GetModelInfos -> GetCustomModels