Correct Param & Var Declarations (#17511)

## Description

For some reason the grammar used "parameter" and "variable" instead of
the actual keywords used in Bicep "param" and "var"

## Checklist

- [x] I have read and adhere to the [contribution
guide](https://github.com/Azure/bicep/blob/main/CONTRIBUTING.md).

###### Microsoft Reviewers: [Open in
CodeFlow](https://microsoft.github.io/open-pr/?codeflow=https://github.com/Azure/bicep/pull/17511)

Author: rgant

docs/grammar.md

@@ -7,9 +7,9 @@ statement ->
   extensionDecl |
   compileTimeImportDecl |
   metadataDecl |
-  parameterDecl |
+  paramDecl |
   typeDecl |
-  variableDecl |
+  varDecl |
   resourceDecl |
   moduleDecl |
   testDecl |
@@ -42,14 +42,14 @@ compileTimeImportFromClause -> "from" interpString(path)
 
 metadataDecl -> "metadata" IDENTIFIER(name) "=" expression NL
 
-parameterDecl ->
-  decorator* "parameter" IDENTIFIER(name) typeExpression parameterDefaultValue? NL |
-  decorator* "parameter" IDENTIFIER(name) "resource" interpString(type) parameterDefaultValue? NL |
+paramDecl ->
+  decorator* "param" IDENTIFIER(name) typeExpression parameterDefaultValue? NL |
+  decorator* "param" IDENTIFIER(name) "resource" interpString(type) parameterDefaultValue? NL |
 parameterDefaultValue -> "=" expression
 
 typeDecl -> decorator* "type" IDENTIFIER(name) "=" typeExpression NL
 
-variableDecl -> decorator* "variable" IDENTIFIER(name) "=" expression NL
+varDecl -> decorator* "var" IDENTIFIER(name) "=" expression NL
 
 resourceDecl -> decorator* "resource" IDENTIFIER(name) interpString(type) "existing"? "=" (ifCondition | object | forExpression) NL