Issues with current Partial

[ice1000]

• The LHS in the clauses are fixed syntax, should be replaced with expr
  

  aya-dev/parser/src/main/grammar/AyaPsiParser.bnf

  Lines 303 to 305 in fb4dbf2

  	cof ::= cofOperand "=" cofOperand
  	private cofOperand ::= refExpr | litIntExpr
  	partialClause ::= cof IMPLIES expr

• When checking the clauses, the LHS cofibration isn't added to the context
  

  aya-dev/base/src/main/java/org/aya/tyck/ExprTycker.java

  Lines 181 to 182 in fb4dbf2

  	var clsCof = elabCof(rcls.cof());
  	var clsRhs = inherit(rcls.tm(), A).wellTyped();

• Based on the first one, if user put weird things in the LHS, we should report an error. We should only allow: ∧, ∨, =, and variables.