query/focusable should be able to provide only-tabbable elements as well

[rodneyrehm]

The following methods ignore elements that are keyboard-focusable but not script-focusable. While this is the expected use case, considering these methods are for scripting, there is currently no way to identify all tabbable elements, e.g. to visually mark them as such.

To allow both uses a new option includeOnlyTabbable: true should be added to the following modules:

• query/first-tabbable
• query/focusable
• query/tabbable
• query/tabsequence

The effect of this option should be to disengage the isOnlyTabbable() constraint in is/focusable. As all elements passing is/only-tabbable must already pass is/focus-relevant, no further change should be necessary.

In #80 the cores of is/focus-relevant and is/tabbable were refactored to allow specifying options, while maintaining the function signatures - the same should be done to is/focusable.

[rodneyrehm]

The initial assumption regarding anything that is considered is/only-focusable is also considered is/focus-relevant is invalid as query/focusable.all considers both.

Missing from is/focus-relevant in Firefox:

[
  "label[tabindex=0]",
  "svg a[xlink|href]",
  "svg[tabindex=-1] a[xlink|href]",
  "svg[focusable=false] a[xlink|href]",
  "svg a[xlink|href][tabindex=0]",
  "svg a[xlink|href][tabindex=1]",
  "svg a[focusable=false]",
  "svg a[xlink|href][tabindex=-1]",
  "svg{tiny} a[focusable=false]",
  "svg{tiny} a[tabindex=-1]",
  "svg{tiny}[focusable=false] a"
]

Missing from is/focus-relevant in Internet Explorer:

[
  "svg",
  "svg a[xlink|href]",
  "svg rect[focusable=true]",
  "svg[tabindex=-1]",
  "svg[tabindex=-1] a[xlink|href]",
  "svg[focusable=false] a[xlink|href]",
  "svg:has(a[tabindex=0])",
  "svg a[xlink|href][tabindex=0]",
  "svg a[xlink|href][tabindex=1]",
  "svg{viewbox}",
  "svg rect[focusable=true]{viewbox}",
  "svg:has(a[tabindex=-1])",
  "svg a[xlink|href][tabindex=-1]",
  "svg{tiny}",
  "svg{tiny} rect[focusable=true]",
  "svg{tiny} a[tabindex=-1]",
  "svg{tiny} rect[focusable=true][tabindex=-1]",
  "svg{tiny}[focusable=false] a"
]

Chrome does not suffer from the is/only-tabbable workaround