[MINOR][ML] Reorg RFormula params.

[yanboliang]

What changes were proposed in this pull request?

There are mainly two reasons for this reorg:

• Some params are placed in RFormulaBase, while others are placed in RFormula, this is disordered.
• RFormulaModel should have params handleInvalid, formula and forceIndexLabel, that users can get invalid values handling policy, formula or whether to force index label if they only have a RFormulaModel. So we need move these params to RFormulaBase which is also inherited by RFormulaModel.
• RFormulaModel should support set different handleInvalid when cross validation.

How was this patch tested?

Existing tests.

[SparkQA]

Test build #79755 has finished for PR 18681 at commit 673d2df.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[yanboliang]

cc @felixcheung

[yanboliang]

Merged into master. Thanks for reviewing.