Bump default theme versions for 5.5

[desrosj]

Looking at the changed files since 5.4.2 (last theme release), each bundled theme has changes and should receive a new version.

Touching multiple themes:

• #39860

Theme specific tickets:

• Twenty Fifteen: #50029.
• Twenty Sixteen: #50180.
• Twenty Seventeen: #39384, #39685, #43999, #44004.
• Twenty Nineteen: #45912, #45876, #45866, #49613, #49843.
• Twenty Twenty: #50421, #50271, #50174, #50109, #49986, #49896, #49833, #49710, #49610, #49600, #49058, #48713.

Previously:

• #49743 (5.4)
• #48944 (5.3.1)
• #47172 (5.2)
• #46070 (5.1)
• #45792 (5.0.3)

[desrosj]

50889.2.diff​ also updates the readme.txt files, and package.json files for newer themes.

[whyisjake]

Adding the dev-feedback tag for 5.5 inclusion.

[SergeyBiryukov]

50889.2.diff​ looks good.

[desrosj]

Committed to trunk in [48775]. Had the incorrect ticket number. Backporting now!

[desrosj]

In 48776:

Bundled Themes: Bump theme versions ahead of WordPress 5.5.

The following theme versions will be released in coordination with WordPress 5.5:

• Twenty Ten: 3.1
• Twenty Eleven: 3.5
• Twenty Twelve: 3.2
• Twenty Thirteen: 3.1
• Twenty Fourteen: 2.9
• Twenty Fifteen: 2.7
• Twenty Sixteen: 2.2
• Twenty Seventeen: 2.4
• Twenty Nineteen: 1.7
• Twenty Twenty: 1.5

Props whyisjake, desrosj.
Reviewed by whyisjake, SergeyBiryukov, desrosj.
Merges [48775] to the 5.5 branch.
Fixes #50889.